U.S. patent application number 14/456275 was filed with the patent office on 2014-11-27 for semiconductor device.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Koichiro KAMATA.
Application Number | 20140347777 14/456275 |
Document ID | / |
Family ID | 44319142 |
Filed Date | 2014-11-27 |
United States Patent
Application |
20140347777 |
Kind Code |
A1 |
KAMATA; Koichiro |
November 27, 2014 |
SEMICONDUCTOR DEVICE
Abstract
To prevent damage on an element even when a voltage high enough
to break the element is input. A semiconductor device of the
invention operates with a first voltage and includes a protection
circuit which changes the value of the first voltage when the
absolute value of the first voltage is higher than a reference
value. The protection circuit includes: a control signal generation
circuit generating a second voltage based on the first voltage and
outputting the generated second voltage; and a voltage control
circuit. The voltage control circuit includes a transistor which
has a source, a drain, and a gate, and which is turned on or off
depending on the second voltage input to the gate and thus controls
whether the value of the first voltage is changed based on the
amount of current flowing between the source and the drain. The
transistor also includes an oxide semiconductor layer.
Inventors: |
KAMATA; Koichiro; (Isehara,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
44319142 |
Appl. No.: |
14/456275 |
Filed: |
August 11, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13012160 |
Jan 24, 2011 |
8816469 |
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14456275 |
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Current U.S.
Class: |
361/119 |
Current CPC
Class: |
H01L 27/0285 20130101;
H02M 1/32 20130101; G06K 19/07749 20130101; H02M 7/217 20130101;
H01L 27/0248 20130101; H02J 7/025 20130101; G06K 19/0701 20130101;
H02H 9/046 20130101; H01L 27/1225 20130101; H02J 50/12 20160201;
G06K 19/0715 20130101 |
Class at
Publication: |
361/119 |
International
Class: |
H02H 9/04 20060101
H02H009/04; H01L 27/02 20060101 H01L027/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2010 |
JP |
2010-019183 |
Claims
1. (canceled)
2. A semiconductor device comprising: a rectifier circuit; and a
protection circuit comprising: a first transistor; a second
transistor; a rectifier element; a first resistor; and a second
resistor, wherein an input terminal of the rectifier circuit is
electrically connected to one of a source and a drain of the second
transistor, wherein an output terminal of the rectifier circuit is
electrically connected to one of a source and a drain of the first
transistor and a first terminal of the second resistor, wherein a
second terminal of the second resistor is electrically connected to
a terminal of the rectifier element and a gate of the first
transistor, wherein the other of the source and the drain of the
first transistor is electrically connected to a terminal of the
first resistor and a gate of the second transistor, wherein a
semiconductor layer of the first transistor includes silicon, and
wherein a semiconductor layer of the second transistor includes an
oxide semiconductor.
3. The semiconductor device according to claim 2, wherein the
semiconductor layer of the second transistor comprises at least one
of indium, gallium, tin, and zinc.
4. The semiconductor device according to claim 2, wherein a band
gap of the semiconductor layer of the second transistor is equal to
or more than 2 eV.
5. The semiconductor device according to claim 2, wherein a carrier
concentration of the semiconductor layer of the second transistor
is less than 1.times.10.sup.14/cm.sup.3.
6. The semiconductor device according to claim 2, wherein the
semiconductor layer of the second transistor comprises a
crystalline region including a c-axis aligned in a direction
perpendicular to a surface of the semiconductor layer of the second
transistor.
7. The semiconductor device according to claim 2, wherein the
rectifier element is a diode or a diode-connected transistor.
8. The semiconductor device according to claim 7, wherein the
diode-connected transistor includes an oxide semiconductor.
9. The semiconductor device according to claim 2, further
comprising a capacitor, wherein a first terminal of the capacitor
is electrically connected to the one of the source and the drain of
the second transistor, and wherein a second terminal of the
capacitor is electrically connected to the input terminal of the
rectifier circuit.
10. A semiconductor device comprising: a rectifier circuit; and a
protection circuit comprising: a first circuit comprising: a first
transistor; a rectifier element; a first resistor; and a second
resistor; and a second circuit comprising: a second transistor,
wherein an input terminal of the rectifier circuit is electrically
connected to the second circuit, wherein an output terminal of the
rectifier circuit is electrically connected to the first circuit,
wherein a terminal of the second resistor is electrically connected
to a terminal of the rectifier element and a gate of the first
transistor, wherein one of a source and a drain of the first
transistor is electrically connected to a terminal of the first
resistor and a gate of the second transistor, wherein a
semiconductor layer of the first transistor includes silicon, and
wherein a semiconductor layer of the second transistor includes an
oxide semiconductor.
11. The semiconductor device according to claim 10, wherein the
semiconductor layer of the second transistor comprises at least one
of indium, gallium, tin, and zinc.
12. The semiconductor device according to claim 10, wherein a band
gap of the semiconductor layer of the second transistor is equal to
or more than 2 eV.
13. The semiconductor device according to claim 10, wherein a
carrier concentration of the semiconductor layer of the second
transistor is less than 1.times.10.sup.14/cm.sup.3.
14. The semiconductor device according to claim 10, wherein the
semiconductor layer of the second transistor comprises a
crystalline region including a c-axis aligned in a direction
perpendicular to a surface of the semiconductor layer of the second
transistor.
15. The semiconductor device according to claim 10, wherein the
rectifier element is a diode or a diode-connected transistor.
16. The semiconductor device according to claim 15, wherein the
diode-connected transistor includes an oxide semiconductor.
17. The semiconductor device according to claim 10, wherein the
second circuit comprises a capacitor, a terminal of the capacitor
is electrically connected to one of a source and a drain of the
second transistor.
18. A semiconductor device comprising: an antenna; a rectifier
circuit electrically connected to the antenna; and a protection
circuit comprising: a first transistor; a second transistor; a
rectifier element; a first resistor; and a second resistor, wherein
an input terminal of the rectifier circuit is electrically
connected to one of a source and a drain of the second transistor,
wherein an output terminal of the rectifier circuit is electrically
connected to one of a source and a drain of the first transistor
and a first terminal of the second resistor, wherein a second
terminal of the second resistor is electrically connected to a
terminal of the rectifier element and a gate of the first
transistor, wherein the other of the source and the drain of the
first transistor is electrically connected to a terminal of the
first resistor and a gate of the second transistor, wherein a
semiconductor layer of the first transistor includes silicon, and
wherein a semiconductor layer of the second transistor includes an
oxide semiconductor.
19. The semiconductor device according to claim 18, wherein the
semiconductor layer of the second transistor comprises at least one
of indium, gallium, tin, and zinc.
20. The semiconductor device according to claim 18, wherein a band
gap of the semiconductor layer of the second transistor is equal to
or more than 2 eV.
21. The semiconductor device according to claim 18, wherein a
carrier concentration of the semiconductor layer of the second
transistor is less than 1.times.10.sup.14/cm.sup.3.
22. The semiconductor device according to claim 18, wherein the
semiconductor layer of the second transistor comprises a
crystalline region including a c-axis aligned in a direction
perpendicular to a surface of the semiconductor layer of the second
transistor.
23. The semiconductor device according to claim 18, wherein the
rectifier element is a diode or a diode-connected transistor.
24. The semiconductor device according to claim 23, wherein the
diode-connected transistor includes an oxide semiconductor.
25. The semiconductor device according to claim 18, further
comprising a capacitor, wherein a first terminal of the capacitor
is electrically connected to the one of the source and the drain of
the second transistor, and wherein a second terminal of the
capacitor is electrically connected to the input terminal of the
rectifier circuit.
26. A semiconductor device comprising: an antenna; a rectifier
circuit electrically connected to the antenna; and a protection
circuit comprising: a first circuit comprising: a first transistor;
a rectifier element; a first resistor; and a second resistor; and a
second circuit comprising: a second transistor, wherein an input
terminal of the rectifier circuit is electrically connected to the
second circuit, wherein an output terminal of the rectifier circuit
is electrically connected to the first circuit, wherein a terminal
of the second resistor is electrically connected to a terminal of
the rectifier element and a gate of the first transistor, wherein
one of a source and a drain of the first transistor is electrically
connected to a terminal of the first resistor and a gate of the
second transistor, wherein a semiconductor layer of the first
transistor includes silicon, and wherein a semiconductor layer of
the second transistor includes an oxide semiconductor.
27. The semiconductor device according to claim 26, wherein the
semiconductor layer of the second transistor comprises at least one
of indium, gallium, tin, and zinc.
28. The semiconductor device according to claim 26, wherein a band
gap of the semiconductor layer of the second transistor is equal to
or more than 2 eV.
29. The semiconductor device according to claim 26, wherein a
carrier concentration of the semiconductor layer of the second
transistor is less than 1.times.10.sup.14/cm.sup.3.
30. The semiconductor device according to claim 26, wherein the
semiconductor layer of the second transistor comprises a
crystalline region including a c-axis aligned in a direction
perpendicular to a surface of the semiconductor layer of the second
transistor.
31. The semiconductor device according to claim 26, wherein the
rectifier element is a diode or a diode-connected transistor.
32. The semiconductor device according to claim 31, wherein the
diode-connected transistor includes an oxide semiconductor.
33. The semiconductor device according to claim 26, wherein the
second circuit comprises a capacitor, a terminal of the capacitor
is electrically connected to one of a source and a drain of the
second transistor.
Description
TECHNICAL FIELD
[0001] One embodiment of the present invention relates to a
semiconductor device.
BACKGROUND ART
[0002] In recent years, semiconductor devices have been developed
which are capable of supplying (also referred to as feeding) power
(also referred to as a power supply voltage) through wireless
communication, and further capable of transmitting and receiving
data (also referred to as data communication) through wireless
communication. For example, if a feeding function through wireless
communication can be added to a portable information medium (e.g.,
a cellular phone) which is an example of the semiconductor devices,
the portable information medium does not need to be connected to an
external power feeding portion and can be fed more easily, for
example, in any environment.
[0003] An individual identification technology utilizing an RFID
(radio frequency identification) tag is known as an example of
semiconductor devices capable of data transmission, data reception,
data storing, data erasing and the like through wireless
communication. The RFID tag is also referred to as an RF tag, a
wireless tag, an electronic tag, or a wireless chip. The RFID tag
is also referred to as an IC tag, an IC chip, or an IC card because
it includes a functional circuit such as an integrated circuit (IC)
for executing authentication or other processing. Data
communication with the semiconductor device is performed by using a
wireless communication device (such as a reader/writer, which is
capable of transmitting and receiving a data signal through
wireless communication). The individual identification technology
using the semiconductor device is used for the production,
management, or the like of an individual object and has been
expected to be applied to personal authentication.
[0004] In general, the semiconductor device does not include in
itself a power generating means and is fed through wireless
communication; thus, the semiconductor device can be fed even at a
distance from a feeding means. The distance over which wireless
communication is possible is also referred to as a communication
distance. In a semiconductor device externally supplied with power,
the feeding efficiency generally tends to decrease as the
communication distance increases. Therefore, semiconductor devices
to which a desired amount of power can be supplied even at a long
communication distance have been researched and developed (see
Patent Document 1).
REFERENCE
Patent Document
[Patent Document 1] Japanese Published Patent Application No.
2006-005651
DISCLOSURE OF INVENTION
[0005] In the case of a semiconductor device capable of wireless
communication over a predetermined distance or longer, however,
when the semiconductor device is fed at a distance shorter than the
predetermined distance, a voltage (also referred to as an
overvoltage) high enough to break an element is input to the
semiconductor device in some cases.
[0006] An object of one embodiment of the present invention is to
prevent damage on an element even when a voltage high enough to
break the element is input through wireless communication.
[0007] One embodiment of the present invention includes a
protection circuit against voltage, so that when a voltage high
enough to break an element is input, the voltage applied to the
element is reduced by using the protection circuit to prevent
damage on the element.
[0008] One embodiment of the present invention is a semiconductor
device operating with a first voltage and including a protection
circuit which changes the value of the first voltage when the
absolute value of the first voltage is higher than a reference
value. The protection circuit includes: a control signal generation
circuit which generates a second voltage in accordance with the
first voltage and outputs the generated second voltage; and a
voltage control circuit. The voltage control circuit includes a
transistor which has a source, a drain, and a gate, and which is
turned on or off depending on the second voltage input as a control
signal to the gate and thus controls whether the value of the first
voltage is changed in accordance with the amount of current flowing
between the source and the drain. The transistor also includes an
oxide semiconductor layer serving as a channel formation layer. The
band gap of the oxide semiconductor layer is equal to or more than
2 eV.
[0009] One embodiment of the present invention is a semiconductor
device including: a rectifier circuit to which a first voltage is
input, and which rectifies the first voltage to generate a second
voltage and outputs the generated second voltage; and a protection
circuit which has a control signal generation circuit and a voltage
control circuit. The control signal generation circuit includes a
divider circuit which divides the second voltage to generate a
third voltage with use of the divided voltage and outputs the
generated third voltage. The voltage control circuit includes a
transistor which has a source, a drain, and a gate, and which is
turned on or off depending on the third voltage input as a control
signal to the gate and thus controls whether the value of the first
voltage is changed in accordance with the amount of current flowing
between the source and the drain. The transistor also includes an
oxide semiconductor layer serving as a channel formation layer. The
band gap of the oxide semiconductor layer is equal to or more than
2 eV.
[0010] One embodiment of the present invention is a semiconductor
device including: an antenna circuit which receives a carrier wave
to generate a first voltage and outputs the generated first
voltage; a rectifier circuit to which the first voltage is input,
and which rectifies the first voltage to generate a second voltage
and outputs the generated second voltage; a protection circuit; and
a power supply voltage generation circuit which generates a power
supply voltage in accordance with the second voltage. The
protection circuit includes a control signal generation circuit and
a voltage control circuit. The control signal generation circuit
includes a divider circuit which divides the second voltage to
generate a third voltage with use of the divided voltage and
outputs the generated third voltage. The voltage control circuit
includes a transistor which has a source, a drain, and a gate, and
which is turned on or off depending on the third voltage input as a
control signal to the gate and thus controls whether the value of
the first voltage is changed in accordance with the amount of
current flowing between the source and the drain. The transistor
also includes an oxide semiconductor layer serving as a channel
formation layer. The band gap of the oxide semiconductor layer is
equal to or more than 2 eV.
[0011] One embodiment of the present invention is a semiconductor
device including: an antenna circuit which receives a carrier wave
to generate a first voltage and outputs the generated first
voltage; a rectifier circuit to which the first voltage is input,
and which rectifies the first voltage to generate a second voltage
and outputs the generated second voltage; a protection circuit; a
power supply voltage generation circuit which generates a power
supply voltage in accordance with the second voltage; a
demodulation circuit which demodulates the received carrier wave to
extract a data signal; a functional circuit to which the data
signal and the power supply voltage are input, and which carries
out processing based on the data signal; and a modulation circuit
which modulates a carrier wave to be transmitted in accordance with
a response signal input from the functional circuit. The protection
circuit includes a control signal generation circuit and a voltage
control circuit. The control signal generation circuit includes a
divider circuit which divides the second voltage to generate a
third voltage with use of the divided voltage and outputs the
generated third voltage. The voltage control circuit includes a
transistor which has a source, a drain, and a gate, and which is
turned on or off depending on the third voltage input as a control
signal to the gate and thus controls whether the value of the first
voltage is changed in accordance with the amount of current flowing
between the source and the drain. The transistor also includes an
oxide semiconductor layer serving as a channel formation layer. The
band gap of the oxide semiconductor layer is equal to or more than
2 eV.
[0012] Note that in this specification, terms with ordinal numbers,
such as "first" and "second", are used in order to avoid confusion
among components, and the terms do not limit the components
numerically.
[0013] According to one embodiment of the present invention, damage
on an element can be prevented even in the case where a voltage
high enough to break the element is input.
BRIEF DESCRIPTION OF DRAWINGS
[0014] In the accompanying drawings:
[0015] FIG. 1 is a block diagram illustrating an example of a
configuration of a semiconductor device in Embodiment 1;
[0016] FIGS. 2A and 2B are circuit diagrams each illustrating an
example of a configuration of a voltage control circuit in
Embodiment 1;
[0017] FIGS. 3A and 3B are circuit diagrams each illustrating an
example of a configuration of a control signal generation circuit
in Embodiment 2;
[0018] FIG. 4 is a circuit diagram illustrating an example of a
configuration of a rectifier circuit in Embodiment 3;
[0019] FIG. 5 is a diagram illustrating an example of a
configuration of a semiconductor device in Embodiment 4;
[0020] FIG. 6 is a diagram illustrating an example of a
configuration of a semiconductor device in Embodiment 4;
[0021] FIG. 7 is a block diagram illustrating an example of a
configuration of a semiconductor device in Embodiment 5;
[0022] FIGS. 8A to 8D are cross-sectional schematic diagrams each
illustrating an example of a structure of a transistor in
Embodiment 6;
[0023] FIGS. 9A to 9E are cross-sectional schematic diagrams
illustrating an example of a method for manufacturing a transistor
in Embodiment 6;
[0024] FIGS. 10A and 10B are cross-sectional schematic diagrams
each illustrating an example of a structure of a plurality of
transistors in Embodiment 7;
[0025] FIGS. 11A to 11F are views each illustrating an example of
an electronic device in Embodiment 8;
[0026] FIGS. 12A to 12D are views each illustrating an information
medium in Embodiment 9; and
[0027] FIGS. 13A to 13C are graphs each illustrating the transient
characteristics of a semiconductor device in Example 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] Hereinafter, embodiments of the present invention will be
described with reference to the drawings. Note that the present
invention is not limited to the following description, and it will
be easily understood by those skilled in the art that various
changes and modifications can be made without departing from the
spirit and scope of the present invention. Thus, the present
invention should not be interpreted as being limited to the
following description of the embodiments.
Embodiment 1
[0029] In this embodiment, a semiconductor device including a
protection circuit will be described.
[0030] First, an example of a configuration of the semiconductor
device in this embodiment will be described with reference to FIG.
1. FIG. 1 is a block diagram illustrating an example of the
configuration of the semiconductor device in this embodiment.
[0031] The semiconductor device illustrated in FIG. 1 includes a
rectifier circuit (also referred to as a RECT) 101 for rectifying
an input voltage, and a protection circuit (also referred to as a
PRO) 102 for controlling the value of the input voltage.
[0032] A voltage V21 is input to the rectifier circuit 101. The
rectifier circuit 101 has a function of rectifying the input
voltage V21 to generate a voltage V22, and outputting the generated
voltage V22.
[0033] The rectifier circuit 101 includes, for example, a rectifier
element. A full-wave rectifier circuit or a half-wave rectifier
circuit can be used as the rectifier circuit 101, for example.
Further, an N-fold voltage rectifier circuit (N is a natural number
of two or more) can also be used as the rectifier circuit 101. Note
that the rectifier circuit 101 is not necessarily provided in the
semiconductor device in this embodiment; for example, it does not
need to be provided in the case where the voltage V21 is a
direct-current voltage. In the case where the rectifier circuit 101
is not provided, the semiconductor device operates with the voltage
V21.
[0034] Note that the voltage V21 is a voltage input through a node
N11 and a node N12, and the voltage V22 is a voltage output through
a node N13 and a node N12. The node N11, the node N12, and the node
N13 are points connected to other elements.
[0035] Note that in general, voltage refers to a difference between
potentials at two points (also referred to as a potential
difference). However, values of a voltage and a potential are both
represented by volt (V) in circuit diagrams and the like in some
cases, so that it is difficult to distinguish between them. Thus,
in this specification, a potential difference between a potential
at one point and a potential to be the reference (also referred to
as a reference potential) is referred to as a voltage at the point
in some cases unless otherwise specified.
[0036] The protection circuit 102 has a function of, when the
absolute value of the voltage V21 is higher than a value to be the
reference (also referred to as a reference value), changing the
value of the voltage V21 input to the rectifier circuit 101 in
accordance with the voltage V22 rectified by the rectifier circuit
101. The reference value can be determined as appropriate depending
on the circuit specification. When the absolute value of the
voltage V21 is higher than the reference value, the value of the
voltage V21 is preferably controlled in accordance with the voltage
V22 so as to be equal to or lower than the reference value.
[0037] Further, an example of a circuit configuration of the
protection circuit 102 will be described with reference to FIG.
1.
[0038] As illustrated in FIG. 1, the protection circuit 102
includes a control signal generation circuit (also referred to as a
CTLG) 121 and a voltage control circuit (also referred to as a
VCTL) 122.
[0039] The control signal generation circuit 121 has a function of
generating, in accordance with the voltage V22, a voltage to be a
control signal CTL31 of the voltage control circuit 122, and
outputting the generated voltage.
[0040] The voltage output as the control signal CTL31 from the
control signal generation circuit 121 is input to the voltage
control circuit 122. The voltage control circuit 122 has a function
of controlling whether the voltage V21 is changed in accordance
with the input control signal CTL31.
[0041] Configuration examples of the voltage control circuit 122
will be described with reference to FIGS. 2A and 2B. FIGS. 2A and
2B are circuit diagrams illustrating configuration examples of the
voltage control circuit in this embodiment.
[0042] The voltage control circuit 122 illustrated in FIGS. 2A and
2B includes at least a transistor 122a.
[0043] Note that in this specification, a transistor is a
field-effect transistor and includes at least a source, a drain,
and a gate.
[0044] The source refers to the entire source electrode and source
wiring, or part of them. In some cases, the source electrode is not
distinguished from the source wiring and a conductive layer having
the functions of both the source electrode and the source wiring is
referred to as a source.
[0045] The drain refers to the entire drain electrode and drain
wiring, or part of them. In some cases, the drain electrode is not
distinguished from the drain wiring and a conductive layer having
the functions of both the drain electrode and the drain wiring is
referred to as a drain.
[0046] The gate refers to the entire gate electrode and gate
wiring, or part of them. In some cases, the gate electrode is not
distinguished from the gate wiring and a conductive layer having
the functions of both the gate electrode and the gate wiring is
referred to as a gate.
[0047] Further, the source and drain of a transistor are switched
depending on the structure, operation conditions, and the like of
the transistor; thus, it is difficult to distinguish between the
source and the drain. Therefore, in this document (such as the
specification, claims, and drawings), one of the source and the
drain of a transistor is referred to as a first terminal and the
other is referred to as a second terminal in some cases. In the
case where the source or the drain is referred to as a first
terminal or a second terminal, the gate is sometimes referred to as
a third terminal.
[0048] The control signal CTL31 is input to a gate of the
transistor 122a and the transistor 122a is turned on or off
depending on the voltage of the input control signal CTL31. The
voltage control circuit 122 illustrated in FIGS. 2A and 2B has a
function of controlling whether the voltage V21 is changed in
accordance with the amount of current flowing between a source and
a drain of the transistor 122a.
[0049] In the voltage control circuit 122 illustrated in FIG. 2A, a
first terminal of the transistor 122a is electrically connected to
the node N11 and a second terminal of the transistor 122a is
electrically connected to the node N12.
[0050] The voltage control circuit 122 illustrated in FIG. 2B
includes a capacitor 122b.
[0051] Note that in this specification, a capacitor includes a
first terminal and a second terminal, and includes a first
electrode serving as part or the whole of the first terminal, a
second electrode serving as part or the whole of the second
terminal, and a dielectric layer in which electric charge is
accumulated when voltage is applied between the first electrode and
the second electrode.
[0052] A first terminal of the capacitor 122b is electrically
connected to the node N11. The capacitor 122b allows reducing the
voltage applied between the source and the drain of the transistor
122a. A resistor may be provided instead of the capacitor 122b.
[0053] Note that in this specification, a resistor includes a first
terminal and a second terminal.
[0054] In the voltage control circuit 122 illustrated in FIG. 2B,
the first terminal of the transistor 122a is electrically connected
to the second terminal of the capacitor 122b and the second
terminal of the transistor 122a is electrically connected to the
node N12.
[0055] Next, a structure of the transistor which can be used as the
transistor 122a will be described below.
[0056] As the transistor 122a, a transistor including an oxide
semiconductor layer which serves as a channel formation layer can
be used for example. The oxide semiconductor layer of the
transistor, which has a function of the channel formation layer, is
highly purified to be an intrinsic (also referred to as an I-type)
or substantially intrinsic semiconductor layer.
[0057] Note that the high purification means at least one of the
following concepts: removal of hydrogen from an oxide semiconductor
layer as much as possible; and reduction of defects, which are
caused by oxygen deficiency in an oxide semiconductor layer, by
supply of oxygen to the oxide semiconductor layer.
[0058] As an oxide semiconductor which can be used for the oxide
semiconductor layer, for example, a four-component metal oxide, a
three-component metal oxide, or a two-component metal oxide can be
given. As the four-component metal oxide, for example, an
In--Sn--Ga--Zn--O-based metal oxide can be used. As the
three-component metal oxide, for example, an In--Ga--Zn--O-based
metal oxide, an In--Sn--Zn--O-based metal oxide, an
In--Al--Zn--O-based metal oxide, a Sn--Ga--Zn--O-based metal oxide,
an Al--Ga--Zn--O-based metal oxide, or a Sn--Al--Zn--O-based metal
oxide can be used. As the two-component metal oxide, for example,
an In--Zn--O-based metal oxide, a Sn--Zn--O-based metal oxide, an
Al--Zn--O-based metal oxide, a Zn--Mg--O-based metal oxide, a
Sn--Mg--O-based metal oxide, an In--Mg--O-based metal oxide, or an
In--Sn--O-based metal oxide can be used. In addition, an
In--O-based metal oxide, a Sn--O-based metal oxide, a Zn--O-based
metal oxide, or the like can also be used as the oxide
semiconductor. The metal oxide that can be used as the oxide
semiconductor may contain SiO.sub.2.
[0059] Moreover, a material represented by InMO.sub.3(ZnO).sub.m
(m>0) can be used as the oxide semiconductor. Here, M denotes
one or more of metal elements selected from Ga, Al, Mn, and Co. For
example, M can be Ga, Ga and Al, Ga and Mn, or Ga and Co. For
example, an oxide semiconductor whose composition formula is
represented by InMO.sub.3 (ZnO).sub.m where M is Ga is referred to
as the In--Ga--Zn--O-based oxide semiconductor described above,
[0060] Furthermore, the band gap of the oxide semiconductor layer
is equal to or more than 2 eV, preferably equal to or more than 2.5
eV, and more preferably equal to or more than 3 eV, which reduces
the number of carriers generated by thermal excitation to a
negligible level. In addition, the amount of impurity such as
hydrogen which might serve as a donor is reduced to a certain
amount or less so that the carrier concentration is less than
1.times.10.sup.14/cm.sup.3, preferably equal to or less than
1.times.10.sup.12/cm.sup.3. That is, the carrier concentration of
the oxide semiconductor layer is reduced to zero or substantially
zero.
[0061] In the aforementioned oxide semiconductor layer, the
avalanche breakdown does not easily occur and the withstand voltage
is high. For example, the band gap of silicon is as narrow as 1.12
eV; thus, electrons are easily generated due the avalanche
breakdown, and the number of electrons which are accelerated to
high speed so as to go over an energy barrier to a gate insulating
layer is increased. In contrast, since the oxide semiconductor used
for the aforementioned oxide semiconductor layer has a band gap of
2 eV or more which is wider than that of silicon, the avalanche
breakdown does not easily occur and resistance to hot-carrier
degradation is higher than that of silicon, and the withstand
voltage is thus high.
[0062] The hot-carrier degradation means, for example,
deterioration of transistor characteristics caused by fixed charge
which is generated when highly-accelerated electrons are injected
into a gate insulating layer in the vicinity of a drain in a
channel; or deterioration of transistor characteristics caused by a
trap level which is formed at the interface of a gate insulating
layer by highly-accelerated electrons. The deterioration of
transistor characteristics is, for example, variations in threshold
voltage or gate leakage. The hot-carrier degradation is caused by
channel-hot-electron injection (also referred to as CHE injection)
or drain-avalanche-hot-carrier injection (also referred to as DAHC
injection).
[0063] Note that the band gap of silicon carbide, which is one of
materials having high withstand voltage, is substantially equal to
that of an oxide semiconductor used for the oxide semiconductor
layer, but electrons are less likely to be accelerated in an oxide
semiconductor because the mobility of the oxide semiconductor is
lower than that of silicon carbide by approximately two orders of
magnitude. Further, an energy barrier between an oxide
semiconductor and a gate insulating layer is larger than a barrier
between silicon carbide, gallium nitride, or silicon and a gate
insulating layer; therefore, the number of electrons injected into
the gate insulating layer is extremely small, whereby hot-carrier
degradation is less likely to be caused and withstand voltage is
higher than in the case of silicon carbide, gallium nitride, or
silicon. The oxide semiconductor has a high withstand voltage even
in an amorphous state.
[0064] Furthermore, the transistor including the oxide
semiconductor layer can have an off-current per micrometer of
channel width of 10 aA/.mu.m (1.times.10.sup.-17 A/.mu.m) or less,
1 aA/.mu.m (1.times.10.sup.-18 A/.mu.m) or less, 10 zA/.mu.m
(1.times.10.sup.-20 A/.mu.m) or less, and further 1 zA/.mu.m
(1.times.10.sup.-21 A/.mu.m) or less.
[0065] As illustrated in FIGS. 2A and 2B, an example of the voltage
control circuit in this embodiment includes at least a transistor.
A control signal is input to a gate of the transistor from a
control signal generation circuit and the transistor is turned on
depending on the input control signal, whereby the value of a
voltage (the voltage V21) input to the semiconductor device in this
embodiment is changed in accordance with the amount of current
flowing between a source and a drain of the transistor.
[0066] In addition, the transistor includes an oxide semiconductor
layer which uses an oxide semiconductor having a higher withstand
voltage than, for example, silicon used for a conventional
transistor. Damage on a protection circuit can be prevented by
using the transistor for the semiconductor device in this
embodiment, resulting in an increase in reliability.
[0067] Next, an example of the operation of the semiconductor
device illustrated in FIG. 1 will be described.
[0068] First, the voltage V21 is input to the rectifier circuit 101
through the node N11 and the node N12.
[0069] In the rectifier circuit 101, the input voltage V21 is
rectified so that the voltage V22 is generated, and then, the
generated voltage V22 is output as an output voltage through the
node N13 and the node N12.
[0070] In the protection circuit 102, the control signal generation
circuit 121 generates a voltage based on the value of the voltage
V22, and the generated voltage is output as a control signal CTL31
to the gate of the transistor 122a in the voltage control circuit
122.
[0071] At this time, the transistor 122a is turned off when the
absolute value of the voltage V22 is equal to or lower than a
reference value.
[0072] In the case where the absolute value of the voltage V22 is
higher than the reference value, the transistor 122a is turned on
and electrical conduction is established between the source and the
drain of the transistor 122a, so that a current flows between the
source and the drain of the transistor 122a and the value of the
voltage V21 is changed accordingly. The amount of change of the
voltage V21 is determined in accordance with the amount of current
flowing between the source and the drain of the transistor 122a. In
other words, the amount of change of the voltage V21 is determined
depending on the value of the voltage V22.
[0073] As described above, the example of the semiconductor device
shown in this embodiment includes a protection circuit against
voltage, so that when the absolute value of an output voltage is
higher than the reference value, the value of an input voltage is
changed in accordance with the output voltage by using the
protection circuit. As a result, damage on an element can be
prevented even in the case where, for example, the value of the
input voltage is so high at a certain time that the element is
broken. In addition, when the absolute value of the output voltage
is higher than the reference value, the input voltage can be
controlled so that the output voltage is converged to a constant
value.
[0074] In the example of the semiconductor device shown in this
embodiment, the protection circuit includes a transistor for
controlling a change in the value of an input voltage, and the
transistor includes an oxide semiconductor layer which serves as a
channel formation layer and has a wide band gap. Since the
transistor has a higher withstand voltage than a conventional
transistor and is less likely to be damaged, the reliability of the
semiconductor device can be improved. Further, the transistor has a
low off-current, which prevents a decrease in the input voltage of
the semiconductor device due to the off-current of the
transistor.
Embodiment 2
[0075] In this embodiment, an example of a configuration of the
control signal generation circuit shown in the above Embodiment 1
will be described.
[0076] The example of the configuration of the control signal
generation circuit in this embodiment will be described with
reference to FIGS. 3A and 3B. FIGS. 3A and 3B are circuit diagrams
illustrating examples of the configuration of the control signal
generation circuit in this embodiment.
[0077] The control signal generation circuit 121 illustrated in
FIG. 3A includes at least a divider circuit 201.
[0078] The divider circuit 201 has a function of dividing the
voltage V22. An example of a configuration of the divider circuit
201 will be described below.
[0079] The divider circuit 201 includes a resistor 211, a rectifier
element 212a, a rectifier element 212b, a rectifier element 212c,
and a rectifier element 212d. Although the control signal
generation circuit 121 illustrated in FIG. 3A includes the four
rectifier elements, the present invention is not limited to this
example; the control signal generation circuit of this embodiment
can include one rectifier element, or K (K is a natural number of
two or more) rectifier elements which are electrically connected in
series to each other in a forward direction.
[0080] The rectifier elements 212a to 212d are electrically
connected in series to each other in a forward direction.
[0081] As the rectifier elements 212a to 212d, for example, a PN
diode, a PIN diode, or a diode-connected field-effect transistor
can be used.
[0082] A first terminal of the resistor 211 is electrically
connected to a cathode of the rectifier element 212d. Note that a
point at which the resistor 211 and the rectifier element 212d are
connected is also referred to as a node N14.
[0083] In the divider circuit 201, the voltage V22 is applied
between an anode of the rectifier element 212a and a second
terminal of the resistor 211.
[0084] Next, an example of the operation of the control signal
generation circuit illustrated in FIG. 3A will be described.
[0085] First, the voltage V22 is divided by the divider circuit
201, whereby the voltage of the node N14 becomes equal to the
divided voltage V22. Note that the value of the voltage of the node
N14 is determined by the value of the voltage V21 and the value of
the voltage V22.
[0086] For example, when the absolute value of the voltage V21 is
equal to or lower than a reference value, any of the rectifier
elements 212a to 212d is brought into a non-conduction state. At
this time, the combined resistance of the rectifier elements 212a
to 212d can be thought to be much higher than the resistance of the
resistor 211; accordingly, the voltage of the node N14 is close to
the potential of the node N12. Note that the reference value is
determined as appropriate by controlling the threshold voltage of
the rectifier elements 212a to 212d, the resistance of the resistor
211, or the like.
[0087] When the absolute value of the voltage V21 is higher than
the reference value, the rectifier elements 212a to 212d are
brought into a conduction state. At this time, the combined
resistance of the rectifier elements 212a to 212d can be thought to
be much lower than the resistance of the resistor 211; accordingly,
the voltage of the node N14 increases. At this time, the voltage of
the node N14 becomes equal to or higher than a value necessary for
the transistor 122a illustrated in FIG. 2A or FIG. 2B to be turned
on.
[0088] Further, the control signal generation circuit illustrated
in FIG. 3A outputs the voltage of the node N14 as the control
signal CTL31 to the gate of the transistor 122a illustrated in FIG.
2A or FIG. 2B. That is an example of the operation of the control
signal generation circuit illustrated in FIG. 3A.
[0089] As illustrated in the example of FIG. 3A, the control signal
generation circuit shown in Embodiment 1 can be formed by using at
least a divider circuit to divide a voltage applied to the divider
circuit, and generating a control signal of the voltage control
circuit shown in Embodiment 1 with use of the divided voltage.
[0090] The control signal generation circuit illustrated in FIG. 3A
can have a configuration in which all the transistors have the same
conductivity type. Consequently, the number of steps can be reduced
as compared to the case of using a plurality of transistors with
different conductivity types, resulting in a reduction in
manufacturing cost.
[0091] Note that the configuration of the control signal generation
circuit of this embodiment is not limited to that illustrated in
FIG. 3A, and can be other configurations. Another configuration of
the control signal generation circuit of this embodiment will be
described with reference to FIG. 3B.
[0092] The control signal generation circuit 121 illustrated in
FIG. 3B includes a divider circuit 202, a transistor 203, and a
resistor 204.
[0093] The divider circuit 202 has a function of dividing the
voltage V22. An example of a configuration of the divider circuit
202 will be described below.
[0094] The divider circuit 202 includes a resistor 221, a rectifier
element 222a, a rectifier element 222b, a rectifier element 222c,
and a rectifier element 222d. Although the control signal
generation circuit 121 illustrated in FIG. 3B includes the four
rectifier elements, the present invention is not limited to this
example; the control signal generation circuit of this embodiment
can include one rectifier element, or K rectifier elements which
are electrically connected in series to each other in a forward
direction.
[0095] The rectifier elements 222a to 222d are electrically
connected in series to each other in a forward direction. An anode
of the rectifier element 222a is electrically connected to a second
terminal of the resistor 221.
[0096] As the rectifier elements 222a to 222d, for example, a PN
diode, a PIN diode, or a diode-connected field-effect transistor
can be used.
[0097] In the divider circuit 202, the voltage V22 is applied
between a first terminal of the resistor 221 and a cathode of the
rectifier element 222d.
[0098] In the control signal generation circuit illustrated in FIG.
3B, the voltage V22 is applied between a first terminal of the
transistor 203 and a second terminal of the resistor 204.
[0099] A gate of the transistor 203 is electrically connected to
the second terminal of the resistor 221.
[0100] As the transistor 203, for example, a transistor including a
single crystal semiconductor can be used.
[0101] A first terminal of the resistor 204 is electrically
connected to a second terminal of the transistor 203. Note that a
point at which the first terminal of the resistor 204 is connected
to the second terminal of the transistor 203 is also referred to as
a node N16.
[0102] Next, an example of the operation of the control signal
generation circuit illustrated in FIG. 3B will be described. Note
that as an example, a p-type transistor is used as the transistor
203.
[0103] First, the voltage V22 is divided by the divider circuit
202, whereby the voltage of a node N15 becomes equal to the divided
voltage V22. Note that the voltage of the node N15 is determined by
the value of the voltage V21 and the value of the voltage V22.
[0104] For example, when the absolute value of the voltage V21 is
equal to or lower than a reference value, any of the rectifier
elements 222a to 222d is brought into a non-conduction state. At
this time, the combined resistance of the rectifier elements 222a
to 222d can be thought to be much higher than the resistance of the
resistor 221; accordingly, the voltage of the node N15 is close to
the potential of the node N11. Note that the reference value is
determined as appropriate by controlling the threshold voltage of
the rectifier elements 222a to 222d, the resistance of the resistor
221, or the like.
[0105] When the absolute value of the voltage V22 is equal to or
lower than the reference value, the transistor 203 is turned off.
At this time, the voltage of the node N16 is substantially equal to
the potential of the node N12.
[0106] When the absolute value of the voltage V22 is higher than
the reference value, the rectifier elements 222a to 222d are
brought into a conduction state. At this time, the combined
resistance of the rectifier elements 222a to 222d can be thought to
be much lower than the resistance of the resistor 221; accordingly,
the voltage of the node N15 decreases to a value necessary for the
transistor 203 to be turned on.
[0107] In addition, when the absolute value of the voltage V22 is
higher than the reference value, the transistor 203 is turned on
and the voltage of the node N16 increases. At this time, the
voltage of the node N16 becomes equal to or higher than a value
necessary for the transistor 122a illustrated in FIG. 2A or FIG. 2B
to be turned on.
[0108] Further, the control signal generation circuit illustrated
in FIG. 3B outputs the voltage of the node N16 as the control
signal CTL31 to the gate of the transistor 122a illustrated in FIG.
2A or FIG. 2B. That is an example of the operation of the control
signal generation circuit illustrated in FIG. 3B.
[0109] The control signal generation circuit illustrated in FIG. 3B
includes the transistor and the resistor in addition to the
configuration of the control signal generation circuit illustrated
in FIG. 3A. The configuration including the transistor makes it
possible to reduce the time for the voltage as the control signal
CTL31 to change to a desired value.
[0110] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 3
[0111] In this embodiment, an example of the rectifier circuit
shown in the above Embodiment 1 will be described.
[0112] First, the example of the configuration of the rectifier
circuit in this embodiment will be described with reference to FIG.
4. FIG. 4 is a circuit diagram illustrating the example of the
configuration of the rectifier circuit in this embodiment.
[0113] The rectifier circuit illustrated in FIG. 4 includes a
rectifier element 111, a rectifier element 112, and a capacitor
113.
[0114] A cathode of the rectifier element 112 is electrically
connected to an anode of the rectifier element 111.
[0115] A first terminal of the capacitor 113 is electrically
connected to a cathode of the rectifier element 111.
[0116] In the rectifier circuit illustrated in FIG. 4, the voltage
V21 is applied between the node N11 and the node N12, and the
voltage V22 is applied between the node N13 and the node N12.
[0117] As the rectifier elements 111 and 112, for example, a PN
diode, a PIN diode, or a diode-connected field-effect transistor
can be used.
[0118] Next, an example of the operation of the rectifier circuit
illustrated in FIG. 4 will be described.
[0119] When the voltage V21 is higher than a reference potential
and the absolute value of a voltage applied to the rectifier
element 111 in a forward direction is higher than the threshold
voltage of the rectifier element 111, the rectifier element 111 is
brought into a conduction state and the rectifier element 112 is
brought into a non-conduction state. At this time, the voltage V21
is rectified by the rectifier element 111 and a charge
corresponding to the potential of the node N11 is accumulated in
the first terminal of the capacitor 113.
[0120] When the voltage V21 is lower than the reference potential
and the absolute value of a voltage applied to the rectifier
element 112 in a forward direction is higher than the threshold
voltage of the rectifier element 112, the rectifier element 112 is
brought into a conduction state and the rectifier element 111 is
brought into a non-conduction state. At this time, the voltage V21
is rectified by the rectifier element 112 and a charge
corresponding to the potential of the node N11 is accumulated in a
second terminal of the capacitor 113. Consequently, a voltage
applied to the capacitor 113 increases to about twice as high as
the voltage V21. The increased voltage becomes the voltage V22.
[0121] As illustrated in the example of FIG. 4, a half-wave voltage
doubler rectifier circuit can be used as the rectifier circuit in
Embodiment 1. The rectifier circuit is not limited to this example;
an N-fold voltage rectifier circuit can be used, and a full-wave
rectifier circuit can also be used.
[0122] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 4
[0123] In this embodiment, a semiconductor device capable of
generating a power supply voltage through wireless communication
will be described as an example of the semiconductor devices shown
in the above embodiments.
[0124] First, an example of a configuration of the semiconductor
device in this embodiment will be described with reference to FIG.
5 and FIG. 6. FIG. 5 and FIG. 6 are diagrams illustrating examples
of the configuration of the semiconductor device in this
embodiment.
[0125] The semiconductor device illustrated in FIG. 5 and FIG. 6
includes an antenna circuit 501 which transmits and receives a
carrier wave, a rectifier circuit 502 which rectifies an input
voltage, a protection circuit 503 which controls the value of the
input voltage, and a power supply voltage generation circuit (also
referred to as a PWRG) 504 which generates a power supply voltage
Vp in accordance with the input voltage.
[0126] The antenna circuit 501 has a function of receiving a
carrier wave, and includes an antenna 511 and a capacitor 512 as
illustrated in FIG. 5 and FIG. 6.
[0127] The carrier wave is an alternate-current signal which is
also referred to as a carrier. With the carrier wave, feeding or
data signal communication is performed. Note that a carrier wave
externally transmitted to the antenna circuit 501 includes a
modulated carrier wave (a modulated wave).
[0128] The antenna 511 includes a first terminal and a second
terminal.
[0129] The capacitor 512 has a function of a resonance capacitor.
Although the capacitor 512 is not necessarily provided in the
semiconductor device in this embodiment, the resonance frequency of
the antenna circuit 501 can be controlled by using the capacitor
512.
[0130] In the semiconductor device illustrated in FIG. 5 and FIG.
6, a capacitor 505 is provided between the antenna circuit 501 and
the rectifier circuit 502. A first terminal of the capacitor 505 is
electrically connected to the first terminal of the antenna 511.
The capacitor 505 has a function of a filter element which removes
a DC component from an output voltage of the antenna circuit 501.
Note that a point at which the first terminal of the capacitor 505
is connected to the first terminal of the antenna 511 is also
referred to as a node N51.
[0131] The rectifier circuit 502 includes a transistor 521, a
transistor 522, and a capacitor 523.
[0132] A first terminal of the transistor 521 is electrically
connected to a second terminal of the capacitor 505, and a second
terminal of the transistor 521 is electrically connected to the
power supply voltage generation circuit 504. Since a gate of the
transistor 521 is electrically connected to the first terminal of
the transistor 521, the transistor 521 has a function of a
rectifier element. Note that a point at which the first terminal of
the transistor 521 is connected to the second terminal of the
capacitor 505 is also referred to as a node N53.
[0133] A first terminal of the transistor 522 is electrically
connected to the first terminal of the transistor 521, and a second
terminal of the transistor 522 is electrically connected to the
second terminal of the antenna 511. Since a gate of the transistor
522 is electrically connected to the second terminal of the
transistor 522, the transistor 522 has a function of a rectifier
element.
[0134] As the transistor 521 and the transistor 522, it is possible
to use, for example, a transistor including an oxide semiconductor
layer which can be applied to the transistor 122a illustrated in
FIG. 2A or FIG. 2B.
[0135] A first terminal of the capacitor 523 is electrically
connected to the second terminal of the transistor 521, and a
second terminal of the capacitor 523 is electrically connected to
the second terminal of the antenna 511.
[0136] The protection circuit 503 includes a resistor 531, a
transistor 532a, a transistor 532b, a transistor 532c, a transistor
532d, a transistor 533, a resistor 534, a capacitor 535, and a
transistor 536.
[0137] A first terminal of the resistor 531 is electrically
connected to the first terminal of the capacitor 523. Note that a
point at which the first terminal of the resistor 531 is connected
to the first terminal of the capacitor 523 is also referred to as a
node N54.
[0138] A first terminal of the transistor 532a is electrically
connected to a second terminal of the resistor 531. Since a gate of
the transistor 532a is electrically connected to the first terminal
of the transistor 532a, the transistor 532a has a function of a
rectifier element. The transistor 532a has n-type conductivity.
[0139] A first terminal of the transistor 532b is electrically
connected to a second terminal of the transistor 532a. Since a gate
of the transistor 532b is electrically connected to the first
terminal of the transistor 532b, the transistor 532b has a function
of a rectifier element. The transistor 532b has n-type
conductivity.
[0140] A first terminal of the transistor 532c is electrically
connected to a second terminal of the transistor 532b. Since a gate
of the transistor 532c is electrically connected to the first
terminal of the transistor 532c, the transistor 532c has a function
of a rectifier element. The transistor 532c has n-type
conductivity.
[0141] A first terminal of the transistor 532d is electrically
connected to a second terminal of the transistor 532c, and a second
terminal of the transistor 532d is electrically connected to the
second terminal of the antenna 511. Since a gate of the transistor
532d is electrically connected to the first terminal of the
transistor 532d, the transistor 532d has a function of a rectifier
element. The transistor 532d has n-type conductivity.
[0142] As the transistors 532a to 532d, it is possible to use, for
example, a transistor including an oxide semiconductor layer which
can be applied to the transistor 122a illustrated in FIG. 2A or
FIG. 2B.
[0143] A first terminal of the transistor 533 is electrically
connected to the first terminal of the capacitor 523, and a gate of
the transistor 533 is electrically connected to the second terminal
of the resistor 531. Note that a point at which the gate of the
transistor 533 is connected to the second terminal of the resistor
531 is also referred to as a node N55. The transistor 533 has
p-type conductivity.
[0144] As the transistor 533, for example, a transistor including a
single crystal semiconductor can be used.
[0145] A first terminal of the resistor 534 is electrically
connected to a second terminal of the transistor 533, and a second
terminal of the resistor 534 is electrically connected to the
second terminal of the antenna 511. Note that a point at which the
first terminal of the resistor 534 is connected to the second
terminal of the transistor 533 is also referred to as a node
N56.
[0146] The capacitor 535 has a function of reducing the voltage
applied between a source and a drain of the transistor 536. A first
terminal of the capacitor 535 is electrically connected to the
first terminal of the antenna 511.
[0147] A first terminal of the transistor 536 is electrically
connected to a second terminal of the capacitor 535, and a second
terminal of the transistor 536 is electrically connected to the
second terminal of the antenna 511. Note that the transistor 536
has n-type conductivity.
[0148] As the transistor 536, it is possible to use, for example, a
transistor including an oxide semiconductor layer which can be
applied to the transistor 122a illustrated in FIG. 2A or FIG.
2B.
[0149] The power supply voltage generation circuit 504 has a
function of smoothing the voltage applied between the node N54 and
the node N52, namely, an output voltage of the rectifier circuit
502, and generating a power supply voltage with use of the smoothed
voltage. Note that the power supply voltage generation circuit 504
may have a DC converter circuit (e.g., a step-up circuit or a
step-down circuit), so that the output voltage of the rectifier
circuit 502 can be converted to a desired voltage with the DC
converter circuit and a power supply voltage can be generated by
smoothing the converted voltage.
[0150] Further, the semiconductor device illustrated in FIG. 6
includes a filter circuit 506, and the filter circuit 506 includes
a resistor 507 and a capacitor 508.
[0151] A first terminal of the resistor 507 is electrically
connected to the second terminal of the transistor 533, and a
second terminal of the resistor 507 is electrically connected to a
gate of the transistor 536.
[0152] A first terminal of the capacitor 508 is electrically
connected to the second terminal of the resistor 507, and a second
terminal of the capacitor 508 is electrically connected to the
second terminal of the antenna 511.
[0153] Although the filter circuit 506 is not necessarily provided
in the semiconductor device in this embodiment, the filter circuit
506 allows reducing the noise of a voltage generated in the antenna
circuit 501.
[0154] Next, an example of the operation of the semiconductor
device illustrated in FIG. 5 will be described as an example of the
operation of the semiconductor device in this embodiment.
[0155] First, a carrier wave is received by the antenna 511.
[0156] When the antenna 511 receives a carrier wave, a voltage V61
is generated between the node N51 and the node N52 in accordance
with the received carrier wave.
[0157] Further, a voltage V62 applied between the node N53 and the
node N52 is changed depending on the voltage V61.
[0158] The voltage V62 is rectified by the rectifier circuit 502
and a rectified voltage V63 is output through the node N54 and the
node N52.
[0159] Then, the voltage V63 is input to the protection circuit
503.
[0160] In the protection circuit 503, the voltage V63 is divided by
the resistor 531 and the transistors 532a to 532d. At this time,
the voltage of the node N55 becomes equal to the divided voltage
V63. The transistor 533 is turned on or off depending on the
voltage of the node N55.
[0161] For example, when the absolute value of the voltage of the
node N55 is equal to or lower than a reference value, the voltage
of the node N55 is close to the potential of the node N54, whereby
the transistor 533 is turned off. At this time, the voltage of the
node N56 is substantially equal to the potential of the node N52
and the transistor 536 is turned off, so that the value of the
voltage V61 is not changed substantially.
[0162] When the absolute value of the voltage of the node N55 is
higher than the reference value, the voltage of the node N55 is
close to the potential of the node N52, whereby the transistor 533
is turned on. At this time, the voltage of the node N56 is
determined by the amount of current flowing between a source and a
drain of the transistor 533, and the transistor 536 is turned on in
accordance with the voltage of the node N56, so that the value of
the voltage V61 is changed. The amount of change of the voltage V61
is determined by the amount of current flowing between a source and
a drain of the transistor 536.
[0163] Further, the voltage V63 is input to the power supply
voltage generation circuit 504.
[0164] In the power supply voltage generation circuit 504, a power
supply voltage Vp is generated with use of the input voltage V63,
and the generated power supply voltage Vp is output. That is an
example of the operation of the semiconductor device illustrated in
FIG. 5.
[0165] As described above, the example of the semiconductor device
in this embodiment generates a power supply voltage through
wireless communication. Since the semiconductor device that is an
example of this embodiment includes a protection circuit, when a
power supply voltage is generated through wireless communication,
damage on an element can be prevented even in the case where a
voltage high enough to break the element is input to the
semiconductor device.
[0166] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 5
[0167] In this embodiment, a semiconductor device capable of
transmitting and receiving signals (also referred to as signal
communication) through wireless communication will be described as
an example of the semiconductor devices shown in the above
embodiments.
[0168] First, an example of a configuration of the semiconductor
device in this embodiment will be described with reference to FIG.
7. FIG. 7 is a block diagram illustrating an example of the
configuration of the semiconductor device in this embodiment.
[0169] The semiconductor device illustrated in FIG. 7 includes an
antenna circuit 701 which transmits and receives a carrier wave, a
rectifier circuit 702 which rectifies an input voltage, a
protection circuit 703 which controls the value of the input
voltage, a power supply voltage generation circuit 704 which
generates a power supply voltage in accordance with the input
voltage, a demodulation circuit (also referred to as DMOD) 705
which demodulates a voltage signal based on the carrier wave
received by the antenna circuit 701, a functional circuit (also
referred to as FUNC) 706 which operates with a power supply voltage
and carries out processing based on the voltage signal demodulated
by the demodulation circuit 705, and a modulation circuit (also
referred to as MOD) 707 which modulates a carrier wave to be
transmitted in accordance with the response signal.
[0170] The antenna circuit 701 has a function of transmitting and
receiving a carrier wave.
[0171] A voltage based on the carrier wave received by the antenna
circuit 701 is input to the rectifier circuit 702. The rectifier
circuit 702 has a function of rectifying the voltage.
[0172] The voltage rectified by the rectifier circuit 702 is input
to the protection circuit 703. The protection circuit 703 has a
function of controlling the value of a voltage input to the
rectifier circuit 702 in accordance with in accordance with the
input voltage.
[0173] As the rectifier circuit 702 and the protection circuit 703,
the rectifier circuit and the protection circuit in any of the
semiconductor devices shown in the above embodiments can be
used.
[0174] The voltage rectified by the rectifier circuit 702 is input
to the power supply voltage generation circuit 704. The power
supply voltage generation circuit 704 has a function of generating
a power supply voltage Vp in accordance with the input voltage.
[0175] The demodulation circuit 705 has a function of demodulating
the carrier wave received by the antenna circuit 701 to extract a
data signal.
[0176] The data signal is input from the demodulation circuit 705
to the functional circuit 706. The functional circuit 706 has a
function of carrying out processing based on the data signal.
[0177] The functional circuit 706 includes, for example, a memory
in which specific data or the like is stored, a memory controller
which controls the access to the memory, a logic circuit which
generates a response signal after the processing based on a
demodulated signal is carried out, and an interface which converts
the response signal in accordance with an external apparatus. These
circuits operate when the power supply voltage Vp is input.
[0178] The response signal is input from the functional circuit 706
to the modulation circuit 707. The modulation circuit 707 has a
function of modulating a carrier wave to be transmitted in
accordance with the response signal as needed.
[0179] Next, an example of the operation of the semiconductor
device illustrated in FIG. 7 will be described.
[0180] First, an externally applied carrier wave is received by the
antenna circuit 701.
[0181] When the antenna circuit 701 receives a carrier wave, a
voltage is generated in accordance with the received carrier
wave.
[0182] The voltage generated in accordance with the carrier wave
received by the antenna circuit 701 is input to the rectifier
circuit 702 and the demodulation circuit 705.
[0183] Then, the rectifier circuit 702 rectifies the input voltage
and outputs the rectified voltage.
[0184] The output voltage of the rectifier circuit 702 is input to
the protection circuit 703.
[0185] When the absolute value of a voltage input to the rectifier
circuit 702 is equal to or lower than a reference value, the value
of a voltage input from the protection circuit 703 to the rectifier
circuit 702 is not changed substantially.
[0186] When the absolute value of the voltage input to the
rectifier circuit 702 is higher than the reference value, the value
of a voltage input from the protection circuit 703 to the rectifier
circuit 702 is changed. The amount of change of the voltage input
to the rectifier circuit 702 at this time is determined by the
voltage input to the rectifier circuit 702 and the voltage output
from the rectifier circuit 702.
[0187] The output voltage of the rectifier circuit 702 is input to
the power supply voltage generation circuit 704.
[0188] The power supply voltage generation circuit 704 generates a
power supply voltage Vp in accordance with the input voltage, and
outputs the generated power supply voltage Vp.
[0189] The power supply voltage Vp is input to the functional
circuit 706.
[0190] The demodulation circuit 705 demodulates the carrier wave
input from the antenna circuit 701 to extract a data signal, and
outputs the extracted data signal.
[0191] The data signal is input to the functional circuit 706.
[0192] The functional circuit 706 operates when the power supply
voltage Vp is supplied, and carries out processing based on the
data signal; further, generates a response signal as needed and
outputs the generated response signal.
[0193] The response signal is input to the modulation circuit
707.
[0194] When the response signal is input to the modulation circuit
707, a carrier wave to be transmitted from the antenna circuit 701
is modulated as needed in accordance with the response signal. That
is an example of the operation of the semiconductor device
illustrated in FIG. 7.
[0195] As illustrated in the example of FIG. 7, the example of the
semiconductor device in this embodiment generates a power supply
voltage through wireless communication, and further carries out
processing based on a received carrier wave with use of the power
supply voltage, generates a response signal as needed, and
modulates a carrier wave to be transmitted in accordance with the
response signal as needed. In addition, the semiconductor device in
this embodiment includes a protection circuit. In general, when a
power supply voltage is generated through wireless communication, a
voltage generated by the antenna circuit is considerably changed
depending on a communication distance or the like. Even in such a
case, damage on an element can be prevented with the protection
circuit.
[0196] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 6
[0197] In this embodiment, an example of the transistor that can be
applied to any of the semiconductor devices shown in the above
embodiments will be described.
[0198] As a structure of the transistor that can be applied to any
of the semiconductor devices shown in the above embodiments, for
example, a top-gate structure or a bottom-gate structure can be
used. As the bottom-gate structure, for example, a staggered
structure or a planar structure can be used.
[0199] Further, the transistor that can be applied to any of the
semiconductor devices shown in the above embodiments may have a
structure including one channel formation region (also referred to
as a single-gate structure), a structure including a plurality of
channel formation regions (also referred to as a multi-gate
structure), or a structure in which two conductive layers are
provided over and under a channel region each with an insulating
layer interposed therebetween (also referred to as a dual-gate
structure).
[0200] An example of a structure of the transistor in this
embodiment will be described with reference to FIGS. 8A to 8D.
FIGS. 8A to 8D are cross-sectional schematic diagrams each
illustrating an example of the structure of the transistor in this
embodiment.
[0201] The transistor illustrated in FIG. 8A is one of bottom-gate
transistors, which is also referred to as an inverted staggered
transistor.
[0202] The transistor illustrated in FIG. 8A includes a conductive
layer 401a serving as a gate electrode, an insulating layer 402a
serving as a gate insulating layer, an oxide semiconductor layer
403a serving as a channel formation layer, and a conductive layer
405a and a conductive layer 406a serving as a source or drain
electrode.
[0203] The conductive layer 401a is provided over a substrate 400a,
the insulating layer 402a is provided over the conductive layer
401a, the oxide semiconductor layer 403a is provided over the
conductive layer 401a with the insulating layer 402a interposed
therebetween, and the conductive layer 405a and the conductive
layer 406a are each provided over part of the oxide semiconductor
layer 403a.
[0204] Further, in the transistor illustrated in FIG. 8A, an oxide
insulating layer 407a is in contact with part of a top surface of
the oxide semiconductor layer 403a (part of the oxide semiconductor
layer 403a over which the conductive layer 405a and the conductive
layer 406a are not provided). A protective insulating layer 409a is
provided over the oxide insulating layer 407a.
[0205] The transistor illustrated in FIG. 8B is a channel
protective (also referred to as a channel stop) transistor which is
one of the bottom-gate transistors, and is also referred to as an
inverted staggered transistor.
[0206] The transistor illustrated in FIG. 8B includes a conductive
layer 401b serving as a gate electrode, an insulating layer 402b
serving as a gate insulating layer, an oxide semiconductor layer
403b serving as a channel formation layer, an insulating layer 427
serving as a channel protective layer, and a conductive layer 405b
and a conductive layer 406b serving as a source or drain
electrode.
[0207] The conductive layer 401b is provided over a substrate 400b,
the insulating layer 402b is provided over the conductive layer
401b, the oxide semiconductor layer 403b is provided over the
conductive layer 401b with the insulating layer 402b interposed
therebetween, the insulating layer 427 is provided over the
conductive layer 401b with the insulating layer 402b and the oxide
semiconductor layer 403b interposed therebetween, and the
conductive layer 405b and the conductive layer 406b are each
provided over part of the oxide semiconductor layer 403b with the
insulating layer 427 interposed therebetween.
[0208] Further, a protective insulating layer 409b is in contact
with a top part of the transistor illustrated in FIG. 8B.
[0209] The transistor illustrated in FIG. 8C is one of the
bottom-gate transistors.
[0210] The transistor illustrated in FIG. 8C includes a conductive
layer 401c serving as a gate electrode, an insulating layer 402c
serving as a gate insulating layer, an oxide semiconductor layer
403c serving as a channel formation layer, and a conductive layer
405c and a conductive layer 406c serving as a source or drain
electrode.
[0211] The conductive layer 401c is provided over a substrate 400c,
the insulating layer 402c is provided over the conductive layer
401c, the conductive layer 405c and the conductive layer 406c are
provided over part of the insulating layer 402c, and the oxide
semiconductor layer 403c is provided over the conductive layer 401c
with the insulating layer 402c, the conductive layer 405c, and the
conductive layer 406c interposed therebetween.
[0212] Further, in the transistor illustrated in FIG. 8C, an oxide
insulating layer 407c is in contact with a top surface and a side
surface of the oxide semiconductor layer 403c. In addition, a
protective insulating layer 409c is provided over the oxide
insulating layer 407c.
[0213] The transistor illustrated in FIG. 8D is one of top-gate
transistors.
[0214] The transistor illustrated in FIG. 8D includes a conductive
layer 401d serving as a gate electrode, an insulating layer 402d
serving as a gate insulating layer, an oxide semiconductor layer
403d serving as a channel formation layer, and a conductive layer
405d and a conductive layer 406d serving as a source or drain
electrode.
[0215] The oxide semiconductor layer 403d is provided over a
substrate 400d with a base layer 447 interposed therebetween, the
conductive layer 405d and the conductive layer 406d are each
provided over part of the oxide semiconductor layer 403d, the
insulating layer 402d is provided over the oxide semiconductor
layer 403d, the conductive layer 405d, and the conductive layer
406d, and the conductive layer 401d is provided over the oxide
semiconductor layer 403d with the insulating layer 402d interposed
therebetween.
[0216] Further, in the transistor illustrated in FIG. 8D, the
conductive layer 405d is in contact with a wiring layer 436 through
an opening portion formed in the insulating layer 402d, and the
conductive layer 406d is in contact with a wiring layer 437 through
an opening portion formed in the insulating layer 402d.
[0217] As the substrates 400a to 400d, for example, a glass
substrate such as a barium borosilicate glass substrate or an
aluminoborosilicate glass substrate can be used.
[0218] Alternatively, a substrate formed of an insulator, such as a
ceramic substrate, a quartz substrate, or a sapphire substrate can
be used as the substrates 400a to 400d. Further alternatively,
crystallized glass can be used for the substrates 400a to 400d.
Still further alternatively, a plastic substrate or a semiconductor
substrate of silicon or the like can be used as the substrates 400a
to 400d.
[0219] The base layer 447 has a function of preventing diffusion of
an impurity element from the substrate 400d. As the base layer 447,
a silicon nitride layer, a silicon oxide layer, a silicon nitride
oxide layer, a silicon oxynitride layer, an aluminum oxide layer,
or an aluminum oxynitride layer can be used, for example. The base
layer 447 can also be formed by stacking layers of materials which
can be applied to the base layer 447.
[0220] Note that in the transistors illustrated in FIGS. 8A to 8C,
a base layer may be provided between the substrate and the
conductive layer serving as a gate electrode, as in the transistor
illustrated in FIG. 8D.
[0221] As the conductive layers 401a to 401d, it is possible to
use, for example, a layer of a metal material such as molybdenum,
titanium, chromium, tantalum, tungsten, aluminum, copper,
neodymium, or scandium or an alloy material containing any of these
materials as a main component. The conductive layers 401a to 401d
can also be formed by stacking layers of materials which can be
applied to the conductive layers 401a to 401d.
[0222] As the insulating layers 402a to 402d, a silicon oxide
layer, a silicon nitride layer, a silicon oxynitride layer, a
silicon nitride oxide layer, an aluminum oxide layer, an aluminum
nitride layer, an aluminum oxynitride layer, an aluminum nitride
oxide layer, or a hafnium oxide layer can be used, for example. The
insulating layers 402a to 402d can also be formed by stacking
layers of materials which can be applied to the insulating layers
402a to 402d. The layers of materials which can be applied to the
insulating layers 402a to 402d can be formed by plasma CVD,
sputtering, or the like. For example, the insulating layers 402a to
402d can be formed in such a manner that a silicon nitride layer is
formed by plasma CVD and a silicon oxide layer is formed over the
silicon nitride layer by plasma CVD.
[0223] As an oxide semiconductor which can be used for the oxide
semiconductor layers 403a to 403d, for example, a four-component
metal oxide, a three-component metal oxide, or a two-component
metal oxide can be given. As the four-component metal oxide, for
example, an In--Sn--Ga--Zn--O-based metal oxide can be used. As the
three-component metal oxide, for example, an In--Ga--Zn--O-based
metal oxide, an In--Sn--Zn--O-based metal oxide, an
In--Al--Zn--O-based metal oxide, a Sn--Ga--Zn--O-based metal oxide,
an Al--Ga--Zn--O-based metal oxide, or a Sn--Al--Zn--O-based metal
oxide can be used. As the two-component metal oxide, for example,
an In--Zn--O-based metal oxide, a Sn--Zn--O-based metal oxide, an
Al--Zn--O-based metal oxide, a Zn--Mg--O-based metal oxide, a
Sn--Mg--O-based metal oxide, an In--Mg--O-based metal oxide, or an
In--Sn--O-based metal oxide can be used. In addition, an
In--O-based metal oxide, a Sn--O-based metal oxide, a Zn--O-based
metal oxide, or the like can also be used as the oxide
semiconductor. The metal oxide that can be used as the oxide
semiconductor may contain SiO.sub.2. Here, for example, the
In--Ga--Zn--O-based metal oxide means an oxide containing at least
In, Ga, and Zn, and the composition ratio of the elements is not
particularly limited. The In--Ga--Zn--O-based metal oxide may
contain an element other than In, Ga, and Zn.
[0224] Further, as an oxide semiconductor which can be used for the
oxide semiconductor layers 403a to 403d, a metal oxide represented
by a chemical formula InMO.sub.3(ZnO).sub.m (m>0, and m is not a
natural number) can be used. Here, M denotes one or more of metal
elements selected from Ga, Al, Mn, and Co. For example, M can be
Ga, Ga and Al, Ga and Mn, or Ga and Co.
[0225] As the conductive layers 405a to 405d and the conductive
layers 406a to 406d, a layer of a metal material such as aluminum,
chromium, copper, tantalum, titanium, molybdenum, or tungsten or an
alloy material containing any of the metal materials as a main
component can be used, for example. The conductive layers 405a to
405d and the conductive layers 406a to 406d can also be formed by
stacking layers of materials which can be applied to the conductive
layers 405a to 405d and the conductive layers 406a to 406d.
[0226] For example, the conductive layers 405a to 405d and the
conductive layers 406a to 406d can be formed by stacking a metal
layer of aluminum or copper and a high-melting-point metal layer of
titanium, molybdenum, tungsten, or the like. The conductive layers
405a to 405d and the conductive layers 406a to 406d may have a
structure in which a metal layer of aluminum or copper is provided
between a plurality of high-melting-point metal layers. Further,
when the conductive layers 405a to 405d and the conductive layers
406a to 406d are formed using an aluminum layer to which an element
that prevents generation of hillocks or whiskers (e.g., Si, Nd, or
Si) is added, heat resistance can be increased.
[0227] Alternatively, the conductive layers 405a to 405d and the
conductive layers 406a to 406d can be formed using a layer
containing a conductive metal oxide. As the conductive metal oxide,
indium oxide (In.sub.2O.sub.3), tin oxide (SnO.sub.2), zinc oxide
(ZnO), an alloy of indium oxide and tin oxide
(In.sub.2O.sub.3--SnO.sub.2, abbreviated to ITO), an alloy of
indium oxide and zinc oxide (In.sub.2O.sub.3--ZnO), or such a metal
oxide material containing silicon oxide can be used, for
example.
[0228] Furthermore, another wiring may be formed using the material
used to form the conductive layers 405a to 405d and the conductive
layers 406a to 406d.
[0229] As the wiring layer 436 and the wiring layer 437, a layer of
a material which can be applied to the conductive layers 405a to
405d and the conductive layers 406a to 406d can be used. The wiring
layer 436 and the wiring layer 437 can also be formed by stacking
layers of materials which can be applied to the wiring layer 436
and the wiring layer 437.
[0230] As the insulating layer 427, a layer which can be applied to
the base layer 447 can be used, for example. The insulating layer
427 can also be formed by stacking layers of materials which can be
applied to the insulating layer 427.
[0231] As the oxide insulating layer 407a and the oxide insulating
layer 407c, an oxide insulating layer such as a silicon oxide layer
can be used. The oxide insulating layer 407a and the oxide
insulating layer 407c can also be formed by stacking layers of
materials which can be applied to the oxide insulating layer 407a
and the oxide insulating layer 407c.
[0232] As the protective insulating layers 409a to 409c, an
inorganic insulating layer such as a silicon nitride layer, an
aluminum nitride layer, a silicon nitride oxide layer, or an
aluminum nitride oxide layer can be used, for example. The
protective insulating layers 409a to 409c can also be formed by
stacking layers of materials which can be applied to the protective
insulating layers 409a to 409c.
[0233] Note that in the semiconductor devices in the above
embodiments, in order to reduce surface unevenness due to the
transistor of this embodiment, a planarization insulating layer can
be provided over the transistor (in the case where the transistor
includes an oxide insulating layer or a protective insulating
layer, over the transistor with the oxide insulating layer or the
protective insulating layer interposed therebetween). As the
planarization insulating layer, a layer of an organic material such
as polyimide, acrylic, or benzocyclobutene can be used.
Alternatively, a layer of a low-dielectric constant material (a
low-k material) can be used as the planarization insulating layer.
The planarization insulating layer can also be formed by stacking
layers of materials which can be applied to the planarization
insulating layer.
[0234] Next, as an example of a method for manufacturing the
transistor in this embodiment, an example of a method for
manufacturing the transistor illustrated in FIG. 8A will be
described with reference to FIGS. 9A to 9E. FIGS. 9A to 9E are
cross-sectional schematic diagrams illustrating an example of the
manufacturing method of the transistor illustrated in FIG. 8A.
Although an example of the manufacturing method of the transistor
illustrated in FIG. 8A will be shown as an example of the method
for manufacturing the transistor in this embodiment, the present
invention is not limited to this example. For example, as for the
components of FIGS. 8B to 8D which have the same designations as
the components of FIG. 8A and whose function is at least partly the
same as that of the components of FIG. 8A, description of the
example of the manufacturing method of the transistor illustrated
in FIG. 8A can be referred to as appropriate.
[0235] First, the substrate 400a is prepared, and a first
conductive film is formed over the substrate 400a.
[0236] A glass substrate is used as an example of the substrate
400a.
[0237] As the first conductive film, a film of a metal material
such as molybdenum, titanium, chromium, tantalum, tungsten,
aluminum, copper, neodymium, or scandium, or an alloy material
which contains any of the metal materials as a main component can
be used. The first conductive film can also be formed by stacking
layers of materials which can be applied to the first conductive
film.
[0238] Next, a first photolithography process is carried out: a
first resist mask is formed over the first conductive film, the
first conductive film is selectively etched with use of the first
resist mask to form the conductive layer 401a, and the first resist
mask is removed.
[0239] Note that in this embodiment, the resist mask may be formed
by an ink-jet method. Formation of the resist mask by an inkjet
method needs no photomask; thus, manufacturing cost can be
reduced.
[0240] In order to reduce the number of photomasks and steps in the
photolithography process, the etching step may be performed using a
resist mask formed with a multi-tone mask. The multi-tone mask is a
mask through which light is transmitted to have a plurality of
intensities. A resist mask formed with use of the multi-tone mask
has a plurality of thicknesses and further can be changed in shape
by etching; therefore, the resist mask can be used in a plurality
of etching steps for processing into different patterns. Therefore,
a resist mask corresponding to at least two kinds of different
patterns can be formed with one multi-tone mask. Thus, the number
of light-exposure masks can be reduced and the number of
corresponding photolithography steps can also be reduced, whereby a
manufacturing process can be simplified.
[0241] Next, the insulating layer 402a is formed over the
conductive layer 401a.
[0242] For example, the insulating layer 402a can be formed by
high-density plasma CVD. For example, high-density plasma CVD is
preferably performed using microwaves (e.g., microwaves with a
frequency of 2.45 GHz) in order to form a dense insulating layer
having high withstand voltage and high quality. When the oxide
semiconductor layer is in contact with the high-quality insulating
layer formed by high-density plasma CVD, the interface state can be
reduced and good interface characteristics can be obtained.
[0243] The insulating layer 402a can also be formed by another
method such as sputtering or plasma CVD. Further, heat treatment
may be performed after the formation of the gate insulating layer
402a. The heat treatment can improve the quality of the insulating
layer 402a and the interface characteristics between the insulating
layer 402a and the oxide semiconductor.
[0244] Next, an oxide semiconductor film 530 having a thickness of
2 nm to 200 nm inclusive, preferably 5 nm to 30 nm inclusive is
formed over the insulating layer 402a. For example, the oxide
semiconductor film 530 can be formed by sputtering.
[0245] Note that before the formation of the oxide semiconductor
film 530, powdery substances (also referred to as particles or
dust) attached on a surface of the insulating layer 402a are
preferably removed by reverse sputtering in which an argon gas is
introduced and plasma is generated. The reverse sputtering refers
to a method in which, without application of voltage to a target
side, an RF power source is used for application of voltage to a
substrate side in an argon atmosphere, so that plasma is generated
to modify a surface of the substrate. Note that instead of argon,
nitrogen, helium, oxygen, or the like may be used.
[0246] For example, the oxide semiconductor film 530 can be formed
using an oxide semiconductor material which can be used as a
material of the oxide semiconductor layer 403a. In this embodiment,
the oxide semiconductor film 530 is formed by sputtering with use
of an In--Ga--Zn--O-based oxide target. A cross-sectional view at
this stage corresponds to FIG. 9A. Alternatively, the oxide
semiconductor film 530 can be formed by sputtering in a rare gas
(typically, argon) atmosphere, an oxygen atmosphere, or a mixed
atmosphere of a rare gas and oxygen.
[0247] As a target for forming the oxide semiconductor film 530 by
sputtering, for example, an oxide target having a composition ratio
of In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO=1:1:1 [molar ratio] can be
used. Without limitation to the above target, an oxide target
having a composition ratio of
In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO=1:1:2 [molar ratio] may be
used, for example. The proportion of the volume of a portion except
for an area occupied by a space and the like with respect to the
total volume of the oxide target (also referred to as the filling
rate) is 90% to 100% inclusive, and preferably 95% to 99.9%
inclusive. The oxide semiconductor film formed using a metal oxide
target having high filling rate has high density.
[0248] Note that as a sputtering gas used for forming the oxide
semiconductor film 530, for example, a high-purity gas from which
an impurity such as hydrogen, water, hydroxyl groups, or hydride is
removed is preferably used.
[0249] Before formation of the oxide semiconductor film 530, it is
preferable that the substrate 400a over which the conductive layer
401a is formed or the substrate 400a over which the conductive
layer 401a and the insulating layer 402a are formed be preheated in
a preheating chamber in the sputtering apparatus, so that an
impurity such as hydrogen or moisture adsorbed on the substrate
400a is eliminated and removed. The preheating can prevent
hydrogen, hydroxyl groups, and moisture from entering the
insulating layer 402a and the oxide semiconductor film 530. Note
that a cryopump is preferably used as an exhaustion unit provided
in the preheating chamber. The preheating treatment may be omitted.
Further, the preheating may be similarly performed before formation
of the oxide insulating layer 407a, on the substrate 400a over
which layers up to the conductive layer 405a and the conductive
layer 406a have been formed.
[0250] When the oxide semiconductor film 530 is formed by
sputtering, the substrate 400a is held inside a film formation
chamber which is kept in a reduced pressure state, and the
substrate temperature is set to 100.degree. C. to 600.degree. C.
inclusive, preferably 200.degree. C. to 400.degree. C. inclusive.
By heating the substrate 400a, the concentration of an impurity
contained in the oxide semiconductor film 530 can be reduced.
Further, heating of the substrate 400a can reduce damage on the
oxide semiconductor film 530 due to sputtering. Then, a sputtering
gas from which hydrogen and moisture are removed is introduced
while remaining moisture in the film formation chamber is removed,
and the above-described target is used; thus, the oxide
semiconductor film 530 is formed over the substrate 400a.
[0251] In order to remove remaining moisture in the film formation
chamber, an entrapment vacuum pump such as a cryopump, an ion pump,
or a titanium sublimation pump is preferably used. Further, the
exhaustion unit may be a turbo pump provided with a cold trap. In
the case where the film formation chamber is exhausted with a
cryopump, a hydrogen atom, a compound containing a hydrogen atom
(such as water), and further preferably, a compound containing a
hydrogen atom and a carbon atom, or the like is removed.
Accordingly, with a cryopump, the concentration of an impurity
contained in the oxide semiconductor film 530 that is formed in the
film formation chamber can be reduced.
[0252] As one example of the film formation conditions, the
following can be employed: the distance between the substrate 400
and the target is 100 mm, the pressure is 0.6 Pa, the
direct-current (DC) power is 0.5 kW, and the atmosphere is an
oxygen atmosphere (the proportion of oxygen flow is 100%). Note
that a pulsed direct-current power supply is preferably used
because powdery substances generated at the time of film formation
can be reduced and the film thickness can be made uniform.
[0253] Next, a second photolithography process is carried out: a
second resist mask is formed over the oxide semiconductor film 530,
the oxide semiconductor film 530 is selectively etched with use of
the second resist mask to process the oxide semiconductor film 530
into an island-shaped oxide semiconductor layer, and the second
resist mask is removed.
[0254] In the case of forming a contact hole in the insulating
layer 402a, the contact hole can be formed at the time of
processing the oxide semiconductor film 530 into the island-shaped
oxide semiconductor layer.
[0255] For example, dry etching, wet etching, or both dry etching
and wet etching can be employed for etching the oxide semiconductor
film 530. As an etchant used for wet etching of the oxide
semiconductor film 530, a mixed solution of phosphoric acid, acetic
acid, and nitric acid can be used, for example. Further, ITO07N
(produced by KANTO CHEMICAL CO., INC.) may also be used.
[0256] Next, the oxide semiconductor layer is subjected to first
heat treatment. Through the first heat treatment, the oxide
semiconductor layer can be dehydrated or dehydrogenated. The
temperature of the first heat treatment is 400.degree. C. to
750.degree. C. inclusive, or equal to or higher than 400.degree. C.
and lower than the strain point of the substrate. Here, the
substrate is put in an electric furnace that is a kind of heat
treatment apparatus and heat treatment is performed on the oxide
semiconductor layer in a nitrogen atmosphere at 450.degree. C. for
one hour, and then the oxide semiconductor layer is not exposed to
the air so that entry of water and hydrogen into the oxide
semiconductor layer is prevented. In this manner, the oxide
semiconductor layer 403a is obtained (see FIG. 9B).
[0257] The heat treatment apparatus is not limited to the electric
furnace and may be the one provided with a device for heating a
process object using heat conduction or heat radiation from a
heating element such as a resistance heating element. For example,
an RTA (rapid thermal annealing) apparatus such as a GRTA (gas
rapid thermal annealing) apparatus or an LRTA (lamp rapid thermal
annealing) apparatus can be used. An LRTA apparatus is an apparatus
for heating a process object by radiation of light (an
electromagnetic wave) emitted from a lamp such as a halogen lamp, a
metal halide lamp, a xenon arc lamp, a carbon arc lamp, a
high-pressure sodium lamp, or a high-pressure mercury lamp. A GRTA
apparatus is an apparatus for heat treatment using a
high-temperature gas. As the high-temperature gas, an inert gas
which does not react with a process object by heat treatment, such
as nitrogen or a rare gas like argon, is used.
[0258] For example, as the first heat treatment, GRTA may be
performed in the following manner. The substrate is transferred to
an inert gas which has been heated to a high temperature of
650.degree. C. to 700.degree. C., heated for several minutes, and
transferred from the heated inert gas.
[0259] Note that in the first heat treatment, it is preferable that
water, hydrogen, and the like be not contained in nitrogen or a
rare gas such as helium, neon, or argon. It is also preferable that
nitrogen or a rare gas such as helium, neon, or argon introduced
into the heat treatment apparatus have a purity of 6N (99.9999%) or
more, preferably, 7N (99.99999%) or more (that is, the impurity
concentration is set to be equal to or lower than 1 ppm,
preferably, equal to or lower than 0.1 ppm).
[0260] After the oxide semiconductor layer is heated by the first
heat treatment, a high-purity oxygen gas, a high-purity N.sub.2O
gas, or ultra-dry air (having a dew point of -40.degree. C. or
lower, preferably -60.degree. C. or lower) may be introduced into
the same furnace. It is preferable that the oxygen gas or the
N.sub.2O gas do not contain water, hydrogen, and the like. The
purity of the oxygen gas or the N.sub.2O gas which is introduced
into the heat treatment apparatus is preferably equal to or more
than 6N, more preferably equal to or more than 7N (i.e., the
impurity concentration of the oxygen gas or the N.sub.2O gas is
preferably equal to or lower than 1 ppm, more preferably equal to
or lower than 0.1 ppm). By the effect of the oxygen gas or the
N.sub.2O gas, oxygen that has been reduced through the step of
eliminating an impurity by the dehydration or dehydrogenation
treatment is supplied; thus, the oxide semiconductor layer 403a is
highly purified.
[0261] The first heat treatment may also be performed on the oxide
semiconductor film 530 that has not been processed into the
island-shaped oxide semiconductor layer. In such a case, the
substrate is taken out of the heating apparatus after the first
heat treatment and then the oxide semiconductor film 530 is
processed into the island-shaped oxide semiconductor layer.
[0262] Other than the above-described timings, the first heat
treatment may be performed after the formation of the oxide
semiconductor layer, for example, after formation of the conductive
layer 405a and the conductive layer 406a over the oxide
semiconductor layer 403a or after formation of the oxide insulating
layer 407a over the conductive layer 405a and the conductive layer
406a.
[0263] In the case of forming a contact hole in the insulating
layer 402a, the contact hole may be formed before the first heat
treatment is performed.
[0264] The oxide semiconductor layer may be formed using an oxide
semiconductor film which is formed through two deposition steps so
as to be a thick film including a crystalline region (a single
crystal region), that is, a crystalline region having a c-axis
aligned in a direction perpendicular to a surface of the film,
regardless of the material of a base component such as an oxide, a
nitride, or a metal. For example, a first oxide semiconductor film
with a thickness of 3 nm to 15 nm inclusive is deposited and
subjected to first heat treatment at a temperature of 450.degree.
C. to 850.degree. C. inclusive, preferably 550.degree. C. to
750.degree. C. inclusive under an atmosphere of nitrogen, oxygen, a
rare gas, or dry air, so that the first oxide semiconductor film
which includes a crystalline region (including a plate-like
crystal) in a region including a surface is formed. Then, a second
oxide semiconductor film that is thicker than the first oxide
semiconductor film is formed and subjected to second heat treatment
at a temperature of 450.degree. C. to 850.degree. C. inclusive,
preferably 600.degree. C. to 700.degree. C. inclusive, so that
crystal growth proceeds toward the upper side from the first oxide
semiconductor film to the second oxide semiconductor film using the
first oxide semiconductor film as a seed of the crystal growth, and
the entire region of the second oxide semiconductor film is
crystallized. Using the film including a crystalline region, which
is thick as a consequence, an oxide semiconductor layer may be
formed.
[0265] Next, a second conductive film is formed over the insulating
layer 402a and the oxide semiconductor layer 403a.
[0266] As the second conductive film, a film of a metal material
such as aluminum, chromium, copper, tantalum, titanium, molybdenum,
or tungsten, or an alloy material which contains any of the metal
materials as a main component can be used, for example. The second
conductive film can also be formed by stacking films of materials
which can be applied to the second conductive film.
[0267] Next, a third photolithography process is carried out: a
third resist mask is formed over the second conductive film, the
second conductive film is selectively etched with use of the third
resist mask to form the conductive layer 405a and the conductive
layer 406a, and the third resist mask is removed (see FIG. 9C).
[0268] Note that another wiring may be formed using the second
conductive film at the time of forming the conductive layer 405a
and the conductive layer 406a.
[0269] In light exposure in forming the third resist mask,
ultraviolet light, KrF laser light, or ArF laser light is
preferably used. A channel length L of the transistor to be
completed later depends on the width of an interval between a
bottom end of the conductive layer 405a and a bottom end of the
conductive layer 406a which are adjacent to each other over the
oxide semiconductor layer 403a. In the case where the channel
length L is less than 25 nm, the light exposure at the time of
forming the third resist mask is preferably performed using extreme
ultraviolet light having an extremely short wavelength of several
nanometers to several tens of nanometers. In light exposure using
extreme ultraviolet light, resolution is high and depth of focus is
large. Therefore, the channel length L of the transistor to be
completed later can be made 10 nm to 1000 nm inclusive, and the use
of the transistor formed through such light exposure enables higher
speed operation of a circuit. In addition, the off-current of the
transistor is extremely low, which results in a reduction in power
consumption.
[0270] In the case of etching the second conductive film, etching
conditions are preferably optimized in order to prevent the oxide
semiconductor layer 403a from being divided by the etching.
However, it is difficult to set the conditions under which only the
second conductive film can be etched and the oxide semiconductor
layer 403a is not etched at all. In some cases, part of the oxide
semiconductor layer 403a is etched at the time of etching the
second conductive film, whereby the oxide semiconductor layer 403a
comes to include a groove portion (depression portion).
[0271] In this embodiment, a titanium film is used as an example of
the second conductive film, an In--Ga--Zn--O-based oxide
semiconductor is used as an example of the oxide semiconductor
layer 403a, and an ammonia hydrogen peroxide solution (a mixture of
ammonia, water, and a hydrogen peroxide solution) is used as an
etchant.
[0272] Next, the oxide insulating layer 407a is formed over the
oxide semiconductor layer 403a, the conductive layer 405a, and the
conductive layer 406a. At this time, the oxide insulating layer
407a is in contact with part of the top surface of the oxide
semiconductor layer 403a.
[0273] The oxide insulating layer 407a can be formed to a thickness
of at least 1 nm or more using a method by which impurities such as
water or hydrogen are not introduced into the oxide insulating
layer 407a, such as a sputtering method, as appropriate. When
hydrogen is contained in the oxide insulating layer 407a, entry of
the hydrogen to the oxide semiconductor layer, or extraction of
oxygen in the oxide semiconductor layer by the hydrogen is caused,
thereby causing the backchannel of the oxide semiconductor layer to
have lower resistance (to have an n-type conductivity), so that a
parasitic channel may be formed. Therefore, in order to form the
oxide insulating layer 407a containing as little hydrogen as
possible, it is important to employ a formation method in which
hydrogen is not used.
[0274] In this embodiment, as the oxide insulating layer 407a, a
silicon oxide film having a thickness of 200 nm is formed by
sputtering. The substrate temperature at the time of the film
formation may be room temperature to 300.degree. C. inclusive; in
this embodiment, 100.degree. C. as an example. The formation of a
silicon oxide film by sputtering can be performed in a rare gas
(typically, argon) atmosphere, an oxygen atmosphere, or a mixed
atmosphere of a rare gas and oxygen.
[0275] Further, a silicon oxide target or a silicon target can be
used as a target for forming the oxide insulating layer 407a. For
example, with use of a silicon target, a silicon oxide film can be
formed by sputtering under an atmosphere containing oxygen.
[0276] In order to remove remaining moisture in a film formation
chamber that is used for forming the oxide insulating layer 407a,
an entrapment vacuum pump (such as a cryopump) is preferably used,
for example. By removing remaining moisture in a film formation
chamber with a cryopump, the concentration of an impurity contained
in the oxide insulating layer 407a can be reduced. As an exhaustion
unit for removing remaining moisture in the film formation chamber
that is used for forming the oxide insulating layer 407a, for
example, a turbo pump provided with a cold trap can be used.
[0277] As a sputtering gas used for forming the oxide semiconductor
film 407a, for example, a high-purity gas from which an impurity
such as hydrogen, water, hydroxyl groups, or hydride is removed is
preferably used.
[0278] Before formation of the oxide insulating layer 407a, plasma
treatment with the use of a gas such as N.sub.2O, N.sub.2, or Ar
may be performed to remove water or the like adsorbed on an exposed
surface of the oxide semiconductor layer 403a. In the case where
plasma treatment is performed, the oxide insulating layer 407a
which is in contact with part of the upper surface of the oxide
semiconductor layer 403a is preferably formed without exposure to
the air.
[0279] Then, second heat treatment (preferably, at a temperature of
200.degree. C. to 400.degree. C. inclusive, for example,
250.degree. C. to 350.degree. C. inclusive) can be performed in an
inert gas atmosphere or in an oxygen gas atmosphere. For example,
the second heat treatment is performed at 250.degree. C. in a
nitrogen atmosphere for one hour. Through the second heat
treatment, heat is applied while part of the upper surface of the
oxide semiconductor layer 403a is in contact with the oxide
insulating layer 407a.
[0280] Through the above-described process, the first heat
treatment is performed on the oxide semiconductor film, so that an
impurity such as hydrogen, moisture, hydroxyl groups, or hydride
(also referred to as a hydrogen compound) can be intentionally
removed from the oxide semiconductor layer, and in addition, oxygen
can be supplied to the oxide semiconductor layer. Therefore, the
oxide semiconductor layer is highly purified.
[0281] Through the above process, the transistor is completed (see
FIG. 9D).
[0282] When a silicon oxide layer having many defects is used as
the oxide insulating layer 407a, the heat treatment after formation
of the silicon oxide layer has an effect of diffusing an impurity
such as hydrogen, moisture, hydroxyl groups, or hydride contained
in the oxide semiconductor layer 403a to the oxide insulating layer
407a, so that the impurity contained in the oxide semiconductor
layer 403a can be further reduced.
[0283] The protective insulating layer 409a may be further formed
over the oxide insulating layer 407a. For example, a silicon
nitride film is formed by RF sputtering. The RF sputtering is
preferably used as a formation method of the protective insulating
layer 409a because it achieves high mass productivity. In this
embodiment, as the protective insulating layer 409a, a silicon
nitride film is formed as an example (see FIG. 9E).
[0284] In this embodiment, the protective insulating layer 409a is
formed in such a manner that the substrate 400a over which layers
up to the oxide insulating layer 407a are formed is heated at a
temperature of 100.degree. C. to 400.degree. C., a sputtering gas
containing high-purity nitrogen from which hydrogen and moisture
are removed is introduced, and a silicon nitride film is formed
with use of a target of a silicon semiconductor. In that case also,
the protective insulating layer 409a is preferably formed while
removing remaining moisture in a treatment chamber, similarly to
the case of forming the oxide insulating layer 407a.
[0285] After formation of the protective insulating layer 409a,
heat treatment may be further performed at a temperature of
100.degree. C. to 200.degree. C. inclusive under the air for 1 hour
to 30 hours inclusive. The heat treatment may be performed at a
fixed heating temperature. Alternatively, the following change in
heating temperature may be conducted plural times repeatedly: an
increase from room temperature to a temperature of 100.degree. C.
to 200.degree. C. inclusive and then a decrease to room
temperature. That is an example of the method for manufacturing the
transistor illustrated in FIG. 8A.
[0286] As described above, the transistor shown in this embodiment
is a transistor including an oxide semiconductor layer as a channel
formation layer. The oxide semiconductor layer used in the
transistor is highly purified by heat treatment and thereby becomes
an i-type or substantially i-type oxide semiconductor layer. Such a
transistor can be used as a transistor having a high withstand
voltage that is used in the semiconductor devices shown in the
above embodiments.
[0287] The highly-purified oxide semiconductor layer includes
extremely few carriers (close to 0). The carrier concentration of
the oxide semiconductor layer is less than
1.times.10.sup.14/cm.sup.3, preferably less than
1.times.10.sup.12/cm.sup.3, and more preferably less than
1.times.10.sup.11/cm.sup.3. Since the number of carriers in the
oxide semiconductor layer is extremely small, the off-current of
the transistor of this embodiment in reverse bias can be reduced.
It is preferable that the off-current be as low as possible. In the
transistor of this embodiment, the off-current per micrometer of
channel width can be made equal to or less than 10 aA/.mu.m
(1.times.10.sup.-17 A/.mu.m), equal to or less than 1 aA/.mu.m
(1.times.10.sup.-18 A/.mu.m), equal to or less than 10 zA/.mu.m
(1.times.10.sup.-20 A/.mu.m), and further equal to or less than 1
zA/.mu.m (1.times.10.sup.-21 A/.mu.m).
[0288] The transistor of this embodiment has a relatively high
field-effect mobility and is capable of high-speed driving.
Therefore, when the transistor of this embodiment is used, for
example, the voltage input to the semiconductor device can be
controlled more quickly.
[0289] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 7
[0290] In this embodiment, an example of a plurality of transistors
that can be applied to any of the semiconductor devices shown in
the above embodiments will be described.
[0291] An example of a structure of a plurality of transistors in
this embodiment which can be applied to any of the semiconductor
devices shown in the above embodiments will be described with
reference to FIGS. 10A and 10B. FIGS. 10A and 10B are
cross-sectional schematic diagrams each illustrating an example of
the structure of the plurality of transistors in this
embodiment.
[0292] The structure illustrated in FIG. 10A includes a transistor
601a and a transistor 602a.
[0293] The transistor 601a is provided over a substrate 600 with an
insulating layer 603, an insulating layer 604, and an insulating
layer 605 interposed therebetween.
[0294] Further, the transistor 601a includes a semiconductor layer
611 serving as a channel formation layer, an insulating layer 617a
serving as a gate insulating layer, a conductive layer 618a serving
as a gate electrode, and an insulating layer 619a and an insulating
layer 620a each serving as a sidewall insulating layer.
[0295] The semiconductor layer 611 is provided over the substrate
600 with the insulating layer 603, the insulating layer 604, and
the insulating layer 605 interposed therebetween, the insulating
layer 617a is provided over the semiconductor layer 611, the
conductive layer 618a is provided over the semiconductor layer 611
with the insulating layer 617a interposed therebetween, and the
insulating layer 619a and the insulating layer 620a are provided in
contact with side surfaces of the conductive layer 618a.
[0296] Furthermore, the semiconductor layer 611 includes a channel
formation region 612 under the conductive layer 618a, an impurity
region 613a and an impurity region 614a serving as a source or
drain region, a high-resistance impurity region 615a between the
channel formation region 612 and the impurity region 613a, and a
high-resistance impurity region 616a between the channel formation
region 612 and the impurity region 614a.
[0297] The transistor 602a is provided over a top surface of the
transistor 601a with an insulating layer 621a, an insulating layer
622a serving as a planarization layer, and an insulating layer 623a
interposed therebetween. As the transistor 602a, for example, any
of the transistors shown in the above Embodiment 6 can be used. As
an example of the transistor 602a, FIG. 10A illustrates the
transistor having the structure illustrated in FIG. 8A.
[0298] A conductive layer 626a serving as one of a source electrode
and a drain electrode of the transistor 602a is in contact with the
impurity region 614a through an opening formed in the insulating
layer 621a, the insulating layer 622a, and the insulating layer
623a. Note that the conductive layer 626a may be in contact with
the impurity region 614a via a plurality of conductive layers.
[0299] A conductive layer 625a which is formed on the same layer as
the conductive layer 626a serving as one of the source electrode
and the drain electrode of the transistor 602a is in contact with
the impurity region 613a through an opening formed in the
insulating layer 621a, the insulating layer 622a, and the
insulating layer 623a. Note that the conductive layer 625a may be
in contact with the impurity region 613a via a plurality of
conductive layers.
[0300] Further, in the transistor 602a, an oxide insulating layer
627a is in contact with part of a top surface of an oxide
semiconductor layer serving as a channel formation layer (part of
the oxide semiconductor layer over which conductive layers serving
as a source or drain electrode are not provided). A protective
insulating layer 628a is provided over the oxide insulating layer
627a.
[0301] The structure illustrated in FIG. 10B includes a transistor
601b and a transistor 602b.
[0302] The transistor 601b includes a semiconductor substrate 610
having a channel formation region, an insulating layer 617b serving
as a gate insulating layer, a conductive layer 618b serving as a
gate electrode, and an insulating layer 619b, an insulating layer
620b, an insulating layer 608, and an insulating layer 609 serving
as sidewall insulating layers.
[0303] The insulating layer 617b is provided over the semiconductor
substrate 610, and the conductive layer 618b is provided over the
semiconductor substrate 610 with the insulating layer 617b
interposed therebetween.
[0304] Further, the semiconductor substrate 610 includes an
insulating layer 606 serving as an isolation insulating layer with
the other elements provided in the semiconductor substrate 610, an
impurity region 613b and an impurity region 614b serving as a
source or drain region, a high-resistance impurity region 615b
between the channel formation region and the impurity region 613b,
and a high-resistance impurity region 616b between the channel
formation region and the impurity region 614b.
[0305] The transistor 602b is provided over a top surface of the
transistor 601b with an insulating layer 621b, an insulating layer
622b, and an insulating layer 623b interposed therebetween. As the
transistor 602b, for example, any of the transistors shown in the
above Embodiment 6 can be used. As an example of the transistor
602b, FIG. 10B illustrates the transistor having the structure
illustrated in FIG. 8A.
[0306] A conductive layer 626b serving as one of the source
electrode and the drain electrode of the transistor 602b is in
contact with the impurity region 614b through an opening formed in
the insulating layer 621b, the insulating layer 622b, and the
insulating layer 623b. Note that the conductive layer 626b may be
in contact with the impurity region 614b via a plurality of
conductive layers.
[0307] A conductive layer 625b which is provided on the same layer
as the conductive layer 626b serving as one of the source electrode
and the drain electrode of the transistor 602b is in contact with
the impurity region 613b through an opening formed in the
insulating layer 621b, the insulating layer 622b, and the
insulating layer 623b. Note that the conductive layer 625b may be
in contact with the impurity region 613b via a plurality of
conductive layers.
[0308] Further, in the transistor 602b, an oxide insulating layer
627b is in contact with part of a top surface of an oxide
semiconductor layer serving as a channel formation layer (part of
the oxide semiconductor layer over which conductive layers serving
as a source or drain electrode are not provided). A protective
insulating layer 628b is provided over the oxide insulating layer
627b.
[0309] As the substrate 600, for example, a glass substrate, a
ceramic substrate, a quartz substrate, a plastic substrate, or a
silicon substrate can be used.
[0310] As the semiconductor substrate 610, for example, a silicon
substrate, a germanium substrate, or a silicon germanium substrate
can be used. The semiconductor substrate 610 may contain an
impurity element imparting p-type conductivity.
[0311] As the insulating layer 603, the insulating layer 604, and
the insulating layer 606, a silicon nitride layer, a silicon oxide
layer, a silicon nitride oxide layer, a silicon oxynitride layer,
an aluminum oxide layer, or an aluminum oxynitride layer can be
used, for example.
[0312] As the insulating layer 605, it is possible to use, for
example, a silicon oxide layer containing hydrogen, a silicon
nitride layer containing hydrogen, a silicon nitride layer
containing oxygen and hydrogen, a silicon oxynitride layer, or a
silicon nitride oxide layer. For example, silicon oxide formed
using organosilane is preferably used as silicon oxide containing
hydrogen. This is because the silicon oxide film formed using
organosilane can increase the bonding strength between the
substrate 600 and the semiconductor layer 611. As organosilane, it
is possible to use, for example, a silicon-containing compound such
as tetraethoxysilane (TEOS, Si(OC.sub.2H.sub.5).sub.4),
tetramethylsilane (TMS, Si(CH.sub.3).sub.4),
tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane
(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane
(SiH(OC.sub.2H.sub.5).sub.3), or tris(dimethylamino)silane
(SiH(N(CH.sub.3).sub.2).sub.3).
[0313] As the semiconductor layer 611, a layer containing one or
both of silicon and germanium can be used, for example. Further, as
the semiconductor layer 611, a single crystal semiconductor layer,
a polycrystalline semiconductor layer, a microcrystalline
semiconductor layer, or an amorphous semiconductor layer can be
used.
[0314] For example, in the case where a single crystal
semiconductor layer is used as the semiconductor layer 611, first,
a single crystal semiconductor substrate is prepared and a damaged
region is formed in the single crystal semiconductor substrate by,
for example, ion irradiation. After the single crystal
semiconductor substrate including the damaged region is bonded to
the substrate 600 with the insulating layers 603 to 605 interposed
therebetween, part of the single crystal semiconductor substrate is
separated from the bonded substrate (the single crystal
semiconductor substrate and the substrate 600) with the damaged
region used as a cleavage surface. Then, the remaining single
crystal semiconductor region on the substrate 600 is selectively
removed by etching or the like, whereby the single crystal
semiconductor layer can be formed.
[0315] The impurity region 613a, the impurity region 613b, the
impurity region 614a, and the impurity region 614b are regions
containing an impurity element which imparts n-type or p-type
conductivity, and formed by, for example, addition of an impurity
element which imparts n-type or p-type conductivity.
[0316] The high-resistance impurity region 615a, the
high-resistance impurity region 615b, the high-resistance impurity
region 616a, and the high-resistance impurity region 616b are
regions having a higher resistance than the impurity region 613a,
the impurity region 613b, the impurity region 614a, and the
impurity region 614b, and are formed by, for example, addition of
an impurity element imparting n-type or p-type conductivity at a
lower concentration than that of the impurity region 613a, the
impurity region 613b, the impurity region 614a, and the impurity
region 614b.
[0317] As the insulating layers 617a and 617b, a silicon oxide
layer, a silicon nitride layer, a silicon oxynitride layer, a
silicon nitride oxide layer, an aluminum oxide layer, an aluminum
nitride layer, an aluminum oxynitride layer, an aluminum nitride
oxide layer, or a hafnium oxide layer can be used, for example. The
insulating layers 617a and 617b can also be formed by stacking
layers of materials which can be applied to the insulating layers
617a and 617b. The layers of materials which can be applied to the
insulating layers 617a and 617b can be formed by plasma CVD,
sputtering, or the like. For example, the insulating layers 617a
and 617b can be formed in such a manner that a silicon nitride
layer is formed by plasma CVD and a silicon oxide layer is formed
over the silicon nitride layer by plasma CVD.
[0318] As the conductive layers 618a and 618b, a layer of a metal
material such as molybdenum, titanium, chromium, tantalum,
tungsten, aluminum, copper, neodymium, or scandium, or an alloy
material which contains any of the metal materials as a main
component can be used. The conductive layers 618a and 618b can also
be formed by stacking layers of materials which can be applied to
the conductive layers 618a and 618b. For example, the conductive
layers 618a and 618b can be formed in such a manner that a
conductive film is formed by sputtering and then the conductive
film is selectively etched.
[0319] As the insulating layer 619a, the insulating layer 619b, the
insulating layer 608, and the insulating layer 609, a silicon
nitride layer, a silicon oxide layer, a silicon nitride oxide
layer, a silicon oxynitride layer, an aluminum oxide layer, or an
aluminum oxynitride layer can be used, for example.
[0320] As the insulating layer 621a and the insulating layer 621b,
a silicon nitride layer, a silicon oxide layer, a silicon nitride
oxide layer, a silicon oxynitride layer, an aluminum oxide layer,
or an aluminum oxynitride layer can be used, for example. The
insulating layer 621a and the insulating layer 621b can also be
formed by stacking layers of materials which can be applied to the
insulating layer 621a and the insulating layer 621b. The insulating
layer 621a and the insulating layer 621b are formed by plasma CVD
or the like.
[0321] As the insulating layer 622a and the insulating layer 622b,
an organic material layer or an inorganic material layer can be
used, for example. The insulating layer 622a and the insulating
layer 622b can also be formed by stacking layers of materials which
can be applied to the insulating layer 622a and the insulating
layer 622b. The insulating layer 622a and the insulating layer 622b
are formed by plasma CVD or the like.
[0322] As the insulating layer 623a and the insulating layer 623b,
a silicon nitride layer, a silicon oxide layer, a silicon nitride
oxide layer, a silicon oxynitride layer, an aluminum oxide layer,
or an aluminum oxynitride layer can be used, for example. The
insulating layer 623a and the insulating layer 623b can also be
formed by stacking layers of materials which can be applied to the
insulating layer 623a and the insulating layer 623b. The insulating
layer 623a and the insulating layer 623b are formed by plasma CVD
or the like.
[0323] As the conductive layer 625a, the conductive layer 625b, the
conductive layer 626a, and the conductive layer 626b, a layer of a
material which can be applied to a conductive layer serving as the
source or drain electrode of the transistor 602a and the transistor
602b can be used, for example. The conductive layer 625a, the
conductive layer 625b, the conductive layer 626a, and the
conductive layer 626b can also be formed by stacking layers of
materials which can be applied to the conductive layer 625a, the
conductive layer 625b, the conductive layer 626a, and the
conductive layer 626b.
[0324] As illustrated in the example of FIGS. 10A and 10B, the
semiconductor devices in the above embodiments can be formed by
using a plurality of transistors having different structures.
Consequently, a transistor with an optimal structure can be
selectively used in accordance with the property of each circuit;
for example, an n-channel transistor and a p-channel transistor can
be selectively manufactured.
[0325] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 8
[0326] In this embodiment, description will be made on an
electronic device including the semiconductor device which is shown
in the above embodiments and is capable of generating a power
supply voltage through wireless communication.
[0327] Examples of a configuration of the electronic device in this
embodiment will be described with reference to FIGS. 11A to 11F.
FIGS. 11A to 11F are views each illustrating an example of the
configuration of the electronic device in this embodiment.
[0328] The electronic device illustrated in FIG. 11A is a personal
digital assistant. The personal digital assistant illustrated in
FIG. 11A includes at least a display portion 1001 and a chip 1003.
The personal digital assistant illustrated in FIG. 11A can be
combined with a touch panel or the like, and can be used as an
alternative to a variety of portable objects. For example, when the
display portion 1001 is provided with an operation portion 1002
using a touch panel, the personal digital assistant can be used as
a cellular phone. As the touch panel, for example, a resistive
touch panel, an infrared touch panel, a capacitive touch panel, or
an optical touch panel can be used. Note that the operation portion
1002 is not necessarily provided in the display portion 1001, and
operation buttons may be provided separately in the personal
digital assistant illustrated in FIG. 11A. Moreover, since the chip
1003 is provided, the personal digital assistant illustrated in
FIG. 11A can generate a power supply voltage through wireless
communication and operate with the generated power supply voltage.
The personal digital assistant is sometimes used in the environment
where power cannot be supplied externally; therefore, the
semiconductor device of one embodiment of the present invention,
which is capable of generating a power supply voltage through
wireless communication, is preferably used for the personal digital
assistant.
[0329] The electronic device illustrated in FIG. 11B is an
information guide terminal including an automotive navigation
system, for example. The information guide terminal illustrated in
FIG. 11B includes at least a display portion 1101 and a chip 1104,
and can also have operation buttons 1102, an external input
terminal 1103, and the like. The in-car temperature changes greatly
in accordance with the outside-air temperature, and sometimes
exceeds 50.degree. C. Since the characteristics of the
semiconductor device shown in the above embodiments hardly change
due to the temperature, the semiconductor device in the above
embodiments is particularly effective under the circumstances where
the temperature greatly changes, such as the inside of a car.
Moreover, since the chip 1104 is provided, the information guide
terminal illustrated in FIG. 11B can generate a power supply
voltage through wireless communication and operate with the
generated power supply voltage. The information guide terminal is
sometimes used in the environment where power cannot be supplied
externally; therefore, the semiconductor device of one embodiment
of the present invention, which is capable of generating a power
supply voltage through wireless communication, is preferably used
for the information guide terminal.
[0330] The electronic device illustrated in FIG. 11C is a laptop
personal computer. The laptop personal computer illustrated in FIG.
11C includes a housing 1201, a display portion 1202, a speaker
1203, an LED lamp 1204, a pointing device 1205, a connection
terminal 1206, a keyboard 1207, and a chip 1208. Since the chip
1208 is provided, the electronic device illustrated in FIG. 11C can
generate a power supply voltage through wireless communication and
operate with the generated power supply voltage. The laptop
personal computer is sometimes used in the environment where power
cannot be supplied externally; therefore, the semiconductor device
of one embodiment of the present invention, which is capable of
generating a power supply voltage through wireless communication,
is preferably used for the laptop personal computer.
[0331] The electronic device illustrated in FIG. 11D is a portable
game machine. The portable game machine illustrated in FIG. 11D
includes a display portion 1301, a display portion 1302, a speaker
1303, a connection terminal 1304, an LED lamp 1305, a microphone
1306, a recording medium reading portion 1307, operation buttons
1308, a sensor 1309, and a chip 1310. Since the chip 1310 is
provided, the portable game machine illustrated in FIG. 11D can
generate a power supply voltage through wireless communication and
operate with the generated power supply voltage. The portable game
machine is sometimes used in the environment where power cannot be
supplied externally; therefore, the semiconductor device of one
embodiment of the present invention, which is capable of generating
a power supply voltage through wireless communication, is
preferably used for the portable game machine.
[0332] The electronic device illustrated in FIG. 11E is an e-book
reader. The e-book reader illustrated in FIG. 11E includes at least
a housing 1401, a housing 1403, a display portion 1405, a display
portion 1407, a hinge 1411, and a chip 1426.
[0333] The housing 1401 and the housing 1403 are connected with the
hinge 1411. The e-book reader illustrated in FIG. 11E can be opened
and closed with the hinge 1411 as an axis. With such a structure,
the e-book reader can be handled like a paper book. The display
portion 1405 is incorporated in the housing 1401 and the display
portion 1407 is incorporated in the housing 1403. The display
portion 1405 and the display portion 1407 may display different
images. For example, one image can be displayed across both the
display portions. With the structure where different images are
displayed on the display portion 1405 and the display portion 1407,
for example, text can be displayed on a display portion on the
right side (the display portion 1405 in FIG. 11E) and graphics can
be displayed on a display portion on the left side (the display
portion 1407 in FIG. 11E).
[0334] In the e-book reader illustrated in FIG. 11E, an operation
portion or the like can be provided in the housing 1401. For
example, the e-book reader illustrated in FIG. 11E may include a
power switch 1421, operation keys 1423, and a speaker 1425. In the
case where an image with a plurality of pages is displayed in the
e-book reader illustrated in FIG. 11E, the pages can be turned with
the operation keys 1423. Furthermore, in the e-book reader
illustrated in FIG. 11E, a keyboard or a pointing device may be
provided in the display portion 1405 and the display portion 1407,
or in the display portion 1405 or the display portion 1407. Also in
the e-book reader illustrated in FIG. 11E, an external connection
terminal (an earphone terminal, a USB terminal, a terminal
connectable to a variety of cables such as an AC adapter and a USB
cable, or the like), a recording medium insertion portion, and the
like may be provided on the back surface or side surface of the
housing 1401 and the housing 1403. In addition, the e-book reader
illustrated in FIG. 11E may have a function of an electronic
dictionary.
[0335] Since the chip 1426 is provided, the e-book reader
illustrated in FIG. 11E can generate a power supply voltage through
wireless communication and operate with the generated power supply
voltage. The e-book reader is sometimes used in the environment
where power cannot be supplied externally; therefore, the
semiconductor device of one embodiment of the present invention,
which is capable of generating a power supply voltage through
wireless communication, is preferably used for the e-book
reader.
[0336] The e-book reader illustrated in FIG. 11E can have a
configuration capable of transmitting and receiving data through
wireless communication. With such a configuration, desired book
data or the like can be purchased and downloaded from an electronic
book server.
[0337] The electronic device illustrated in FIG. 11F is a display.
The display illustrated in FIG. 11F includes a housing 1501, a
display portion 1502, a speaker 1503, an LED lamp 1504, operation
buttons 1505, a connection terminal 1506, a sensor 1507, a
microphone 1508, a support base 1509, and a chip 1510. Since the
chip 1510 is provided, the display illustrated in FIG. 11F can
generate a power supply voltage through wireless communication and
operate with the generated power supply voltage. When the
semiconductor device of one embodiment of the present invention,
which is capable of generating a power supply voltage through
wireless communication, is used for the display, a power supply
terminal or the like does not need to be provided, resulting in a
reduction in the number of wirings and terminals.
[0338] Note that as the chip 1003, the chip 1104, the chip 1208,
the chip 1310, the chip 1426, or the chip 1510, the semiconductor
device shown in the above embodiments, which is capable of
generating a power supply voltage through wireless communication,
can be used.
[0339] As illustrated in the examples of FIGS. 11A to 11F, the
electronic devices in this embodiment can generate a power supply
voltage through wireless communication. With such a configuration,
the electronic devices can be used for a certain period even in the
environment where the electronic devices cannot be connected to a
power feeding means.
[0340] Note that the electronic devices shown in this embodiment
can have a power storage device in which a generated power supply
voltage is stored. Consequently, the electronic devices can be used
for a certain period even without an external power supply,
resulting in an improvement in convenience. As the power storage
device, for example, one or more of a lithium ion secondary
battery, a lithium ion capacitor, an electric double-layer
capacitor, and a redox capacitor can be used. For example, a
lithium ion secondary battery and a lithium ion capacitor can be
used together, whereby a power storage device which can charge or
discharge at high speed and can supply electric power for a long
time can be formed. Note that the power storage device is not
limited to the lithium ion secondary battery. As the power storage
device, a secondary battery in which another alkali metal ion,
alkaline earth metal ion, or the like is used as a mobile ion may
be used. Further, the power storage device is not limited to the
lithium ion capacitor. As the power storage device, a capacitor in
which another alkali metal ion, alkaline earth metal ion, or the
like is used as a mobile ion may be used.
[0341] The application of the semiconductor device in the above
embodiments is not limited to the electronic devices illustrated in
FIGS. 11A to 11F, and for example, the semiconductor device can
also be applied to an electric car.
[0342] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Embodiment 9
[0343] In this embodiment description will be made on an
information medium including the semiconductor device which is
shown in the above embodiments and is capable of transmitting and
receiving signals through wireless communication.
[0344] Examples of a configuration of the information medium in
this embodiment will be described with reference to FIGS. 12A to
12D. FIGS. 12A to 12D are views each illustrating an example of the
configuration of the information medium in this embodiment.
[0345] The information medium illustrated in FIG. 12A is a card
certificate recording personal data. The card certificate
illustrated in FIG. 12A includes a chip 800, so that security
function such as prevention of forgery can be improved. As the card
certificate, for example, driver's licenses, resident cards, or
passports can be given. With high reliability, the chip 800 is
suitable for the card certificate and the like which are used for a
long period.
[0346] The information medium illustrated in FIG. 12B is a ticket
information medium. The ticket information medium illustrated in
FIG. 12B includes a chip 801, so that information other than that
printed on the ticket information medium can be stored in the chip
801. In addition, the chip 801 can improve security function such
as prevention of forgery of the ticket information medium
illustrated in FIG. 12B. Since the chip 801 has high reliability,
for example, a cutoff portion is provided in part of the ticket and
only the chip 801 is cut along the cutoff portion when the ticket
information medium is no longer used, whereby only the chip 801 can
be collected and reused. As the ticket information medium, for
example, paper money, railway tickets, securities, or other tickets
can be given.
[0347] The information medium illustrated in FIG. 12C is a coin
information medium. The coin information medium includes a chip
802, so that information other than that printed on the coin
information medium can be stored in the chip 802. In addition, the
chip 802 can improve security function such as prevention of
forgery of the coin information medium illustrated in FIG. 12C. As
the coin information medium, for example, coins, railway tickets,
securities, or other tickets can be given.
[0348] The information medium illustrated in FIG. 12D is an
article. The article includes a chip 803, so that information other
than that printed on the article can be stored in the chip 803. In
addition, the chip 803 can improve security function such as
prevention of forgery of the article illustrated in FIG. 12D. There
is no particular limitation on the article, and for example,
various articles such as electronic appliances and household
commodities can be given.
[0349] As the chips 800 to 803, for example, the semiconductor
device shown in the above embodiments, which is capable of wireless
communication, can be employed.
[0350] As described above, the information medium in this
embodiment includes a chip capable of wireless communication. With
such a configuration, the specific data of the information medium
including a chip can be read through wireless communication and
utilized. As a result, the information medium can be managed more
easily with higher security.
[0351] Note that this embodiment can be combined with or replaced
by any of the other embodiments, as appropriate.
Example 1
[0352] In this example, an example of the semiconductor device
shown in the above embodiments will be described.
[0353] Semiconductor devices shown in this example are a
semiconductor device having the configuration illustrated in FIG. 5
(also referred to as a configuration A), and a semiconductor device
having a configuration in which the transistor 533 and the resistor
534 illustrated in FIG. 5 are not provided and the node N55 is
electrically connected to the gate of the transistor 536 (also
referred to as a configuration B).
[0354] The operation of each semiconductor device was verified. The
verification results are illustrated in FIGS. 13A to 13C. FIGS. 13A
to 13C are graphs illustrating the transient characteristics of the
semiconductor devices to which a predetermined voltage input. In
FIGS. 13A to 13C, the horizontal axis represents the time when a
predetermined voltage is input to the semiconductor devices, and
the vertical axis represents the value of a voltage applied to the
power supply voltage generation circuit 504. Note that the
verification was performed here on the assumption that the input
voltage was 10 V, the antenna circuit 501 was connected to an AC
power source with a constant value, and the power supply voltage
generation circuit 504 had a constant load. As a comparative
example, the operation of a semiconductor device from which the
protection circuit 503 illustrated in FIG. 5 is removed (also
referred to as a configuration C) was verified.
[0355] FIG. 13A illustrates the transient characteristics of the
semiconductor device with the configuration A, FIG. 13B illustrates
the transient characteristics of the semiconductor device with the
configuration B, and FIG. 13C illustrates the transient
characteristics of the semiconductor device with the configuration
C. The results show that in the semiconductor devices with the
configurations A and B, an increase in the voltage applied to the
power supply voltage generation circuit 504 is suppressed even when
time passes, as compared to in the semiconductor device with the
configuration C. Consequently, it is found that in the
semiconductor devices shown in this example, the protection circuit
prevents application of a high voltage to the power supply
generation circuit.
[0356] This application is based on Japanese Patent Application
serial no. 2010-019183 filed with Japan Patent Office on Jan. 29,
2010, the entire contents of which are hereby incorporated by
reference.
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